Low equivalent series resistance RF filter circuit board for an active implantable medical device

ABSTRACT

A filtered feedthrough assembly includes a ferrule configured to be installed in an AIMD housing. An insulator is disposed within a ferrule opening. A conductive pathway is disposed within a passageway through the insulator. A filter capacitor is disposed on a device side having active and ground electrode plates disposed within a capacitor dielectric k greater than 0 and less than 1,000. A capacitor active metallization is electrically connected to the active electrode plates. A ground capacitor metallization is electrically connected to the ground electrode plates. The filter capacitor is the first filter capacitor electrically connected to the conductive pathway coming from a body fluid side into the device side. An active electrical connection electrically connects the conductive pathway to the capacitor active metallization. A ground electrical connection electrically connects the ground capacitor metallization to the ferrule. The filter capacitor is a flat-through or an X2Y attenuator filter capacitor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. applicationSer. No. 16/827,171, filed on Mar. 23, 2020, now U.S. Pat. No.11,071,858, which is a continuation of U.S. application Ser. No.16/121,716, filed on Sep. 5, 2018, now U.S. Pat. No. 10,596,369, whichis a continuation-in-part to U.S. application Ser. No. 15/943,998, filedon Apr. 3, 2018, now U.S. Pat. No. 10,350,421, which claims priorityfrom U.S. App. Ser. No. 62/646,552, filed on Mar. 22, 2018.

The present application is also a continuation-in-part of U.S.application Ser. No. 15/797,278, filed on Oct. 30, 2017, now U.S. Pat.No. 10,272,253, which is a continuation-in-part of U.S. application Ser.No. 15/704,657, filed on Sep. 14, 2017, now U.S. Pat. No. 10,092,749,which claims priority from U.S. App. Ser. No. 62/552,363, filed on Aug.30, 2017.

The present application is also a continuation-in-part of U.S.application Ser. No. 15/603,521, filed on May 24, 2017, now U.S. Pat.No. 10,272,252, which claims priority from U.S. App. Ser. Nos.62/461,872, filed on Feb. 22, 2017; 62/450,187, filed on Jan. 25, 2017;62/443,011, filed on Jan. 6, 2017; 62/422,064, filed on Nov. 15, 2016;and 62/420,164, filed on Nov. 10, 2016.

The present application is also a continuation-in-part of U.S.application Ser. No. 15/250,210, filed on Aug. 29, 2016, now U.S. Pat.No. 9,931,514, which is a continuation of U.S. application Ser. No.15/163,241, filed on May 24, 2016, now U.S. Pat. No. 9,764,129, which isa continuation-in-part to U.S. application Ser. No. 14/826,229, filed onAug. 14, 2015, now U.S. Pat. No. 9,427,596, which is a continuation ofU.S. application Ser. No. 14/688,302, filed on Apr. 16, 2015, now U.S.Pat. No. 9,757,558, which is a continuation-in-part to U.S. applicationSer. No. 14/202,653, filed on Mar. 10, 2014, now U.S. Pat. No.9,014,808, which is a continuation of U.S. application Ser. No.14/808,849, filed on Nov. 25, 2013, now U.S. Pat. No. 8,855,768, whichclaims priority from U.S. App. Ser. No. 61/841,419, filed on Jun. 30,2013.

The present application is also a continuation-in-part of U.S.application Ser. No. 13/408,020, filed on Feb. 29, 2012, abandoned,which claims priority from U.S. App. Ser. No. 61/448,069, filed on Mar.1, 2011.

The present application is also a continuation-in-part of U.S.application Ser. No. 16/589,752, filed on Oct. 1, 2019, which is acontinuation of Ser. No. 16/004,569, filed on Jun. 11, 2018, now U.S.Pat. No. 11,198,014.

The present application also claims priority to U.S. App. Ser. No.62/979,600 filed on Feb. 21, 2020.

The contents of all the above applications are fully incorporated hereinby these references.

FIELD OF THE INVENTION

This invention generally relates to the problem of RF energy inducedinto implanted leads during medical diagnostic procedures such asmagnetic resonant imaging (MRI), and provides methods and apparatus forredirecting RF energy to locations other than the distal tipelectrode-to-tissue interface. More specifically, the present inventionutilizes either an MLCC chip capacitor, a flat-through filter capacitoror an X2Y attenuator having a dielectric k greater than 0 and less than1,000 to provide electromagnetic interference (EMI) protection tosensitive active implantable medical device (AIMD) electronics.

BACKGROUND OF THE INVENTION

Compatibility of cardiac pacemakers, implantable defibrillators andother types of active implantable medical devices with magneticresonance imaging (MRI) and other types of hospital diagnostic equipmenthas become a major issue. If one proceeds to the websites of the majorcardiac pacemaker manufacturers in the United States, which include St.Jude Medical, Medtronic and Boston Scientific (formerly Guidant), onewill see that the use of MRI is generally contra-indicated for patientswith implanted pacemakers and cardioverter defibrillators. See alsorecent press announcements of the Medtronic Revo MRI pacemaker which wasrecently approved by the U.S. FDA. With certain technical limitations asto scan type and location, this is the first pacemaker designed for MRIscanning. See also:

-   (1) “Safety Aspects of Cardiac Pacemakers in Magnetic Resonance    Imaging”, a dissertation submitted to the Swiss Federal Institute of    Technology Zurich presented by Roger Christoph Luchinger, Zurich    2002;-   (2) “1. Dielectric Properties of Biological Tissues: Literature    Survey”, by C. Gabriel, S. Gabriel and E. Cortout;-   (3) “II. Dielectric Properties of Biological Tissues: Measurements    and the Frequency Range 0 Hz to 20 GHz”, by S. Gabriel, R. W. Lau    and C. Gabriel;-   (4) “III. Dielectric Properties of Biological Tissues: Parametric    Models for the Dielectric Spectrum of Tissues”, by S. Gabriel, R. W.    Lau and C. Gabriel;-   (5) “Advanced Engineering Electromagnetics”, C. A. Balanis, Wiley,    1989; (6) Systems and Methods for Magnetic-Resonance-Guided    Interventional Procedures, U.S. Pat. No. 7,844,319, Susil and    Halperin et al., filed Apr. 15, 2002;-   (7) Multifunctional Interventional Devices for MRI: A Combined    Electrophysiology/MRI Catheter, by, Robert C. Susil, Henry R.    Halperin, Christopher J. Yeung, Albert C. Lardo and Ergin Atalar,    MRI in Medicine, 2002; and-   (8) Multifunctional Interventional Devices for Use in MRI, U.S. Pat.    No. 7,844,534, Susil et al., issued Nov. 30, 2010.    The contents of the foregoing are all incorporated herein by these    references.

However, an extensive review of the literature indicates that, despitebeing contra-indicated, MRI is indeed often used to image patients withpacemaker, neurostimulator and other active implantable medical devices(AIMDs). As such, the safety and feasibility of MRI in patients withcardiac pacemakers is an issue of gaining significance. The effects ofMRI on patients' pacemaker systems have only been analyzedretrospectively in some case reports. There are a number of papers thatindicate that MRI on new generation pacemakers can be conducted up to0.5 Tesla (T). MRI is one of medicine's most valuable diagnostic tools.MRI is, of course, extensively used for imaging, but is also used forinterventional medicine (surgery). In addition, MRI is used in real timeto guide ablation catheters, neurostimulator tips, deep brain probes andthe like. An absolute contra-indication for pacemaker or neurostimulatorpatients means that these patients are excluded from MRI. This isparticularly true of scans of the thorax and abdominal areas. Because ofMRI's incredible value as a diagnostic tool for imaging organs and otherbody tissues, many physicians simply take the risk and go ahead andperform MRI on a pacemaker patient. The literature indicates a number ofprecautions that physicians should take in this case, including limitingthe power of the MRI RF-pulse field (Specific Absorption Rate—SARlevel), programming the pacemaker to fixed or asynchronous pacing mode,and then careful reprogramming and evaluation of the pacemaker andpatient after the procedure is complete. There have been reports oflatent problems with cardiac pacemakers or other AIMDs after an MRIprocedure sometimes occurring many days later. Moreover, there are anumber of recent papers that indicate that the SAR level is not entirelypredictive of the heating that can be found in implanted leads ordevices. For example, for magnetic resonance imaging devices operatingat the same magnetic field strength and also at the same SAR level,considerable variations have been found relative to heating of implantedleads. It is speculated that SAR level alone is not a good predictor ofwhether or not an implanted device or its associated lead system willoverheat.

There are three types of electromagnetic fields used in an MRI unit. Thefirst type is the main static magnetic field designated B₀ which is usedto align protons in body tissue. The field strength varies from 0.5 to3.0 Tesla in most of the currently available MRI units in clinical use.Some of the newer MRI system fields can go as high as 4 to 5 Tesla. Atthe International Society for Magnetic Resonance in Medicine (ISMRM),which was held on 5-6 Nov. 2005, it was reported that certain researchsystems are going up as high as 11.7 Tesla. This is over 100,000 timesthe magnetic field strength of the earth. A static magnetic field caninduce powerful mechanical forces and torque on any magnetic materialsimplanted within the patient. This includes certain components withinthe cardiac pacemaker itself and/or lead systems. It is not likely(other than sudden system shut down) that the static MRI magnetic fieldcan induce currents into the pacemaker lead system and hence into thepacemaker itself. It is a basic principle of physics that a magneticfield must either be time-varying as it cuts across the conductor, orthe conductor itself must move within a specifically varying magneticfield for currents to be induced.

The second type of field produced by magnetic resonance imaging is theRF-pulse field which is generated by a body coil or a head coil. This isused to change the energy state of the protons and elicit MRI signalsfrom tissue. The RF field is homogeneous in the central region and hastwo main components: (1) the electric field is circularly polarized inthe actual plane; and (2) the H field, sometimes generally referred toas the net magnetic field in matter, is related to the electric field byMaxwell's equations and is relatively uniform. In general, the RF fieldis switched on and off during measurements and usually has a frequencyof about 21 MHz to about 500 MHz depending upon the static magneticfield strength. The frequency of the RF pulse for hydrogen scans variesby the Lamour equation with the field strength of the main static fieldwhere: RF-PULSE FREQUENCY in MHz=(42.56) (STATIC FIELD STRENGTH INTESLA). There are also phosphorous and other types of scanners whereinthe Lamour equation would be different. The present invention applies toall such scanners.

The third type of electromagnetic field is the time-varying magneticgradient fields designated B_(X), B_(Y), B_(Z), which are used forspatial localization. These change their strength along differentorientations and operating frequencies on the order of 2-5 kHz. Thevectors of the magnetic field gradients in the X, Y and Z directions areproduced by three sets of orthogonally positioned coils and are switchedon only during the measurements. In some cases, the gradient field hasbeen shown to elevate natural heart rhythms (heart beat). This is notcompletely understood, but it is a repeatable phenomenon. The gradientfield is not considered by many researchers to create any other adverseeffects.

It is instructive to note how voltages and electro-magnetic interference(EMI) are induced into an implanted lead system. At very low frequency(VLF), voltages are induced at the input to the cardiac pacemaker ascurrents circulate throughout the patient's body and create voltagedrops. Because of the vector displacement between the pacemaker housingand, for example, the tip electrode, voltage drop across the resistanceof body tissues may be sensed due to Ohms Law and the circulatingcurrent of the RF signal. At higher frequencies, the implanted leadsystems actually act as antennas wherein voltages (EMFs) are inducedalong their length. These antennas are not very efficient due to thedamping effects of body tissue; however, this can often be offset byextremely high-power fields (such as MRI pulse fields) and/or bodyresonances. At very high frequencies (such as cellular telephonefrequencies), EMI signals are induced only into the first area of theleadwire system (for example, at the header block of a cardiacpacemaker). This has to do with the wavelength of the signals involvedwherein the signals couple efficiently into the system.

Magnetic field coupling into an implanted lead system is based on loopareas. For example, in a cardiac pacemaker unipolar lead, there is aloop formed by the lead as it comes from the cardiac pacemaker housingto its distal tip electrode, for example, located in the rightventricle. The return path is through body fluid and tissue generallystraight from the tip electrode in the right ventricle back up to thepacemaker case or housing. This forms an enclosed area which can bemeasured from patient X-rays in square centimeters. The average looparea is 200 to 225 square centimeters. This is an average and is subjectto great statistical variation. For example, in a large adult patientwith an abdominal pacemaker implant, the implanted loop area is muchlarger (around 400 square centimeters).

Relating now to the specific case of MRI, the magnetic gradient fieldsare induced through enclosed loop areas. However, the RF-pulse fieldsgenerated by the body coil are primarily induced into the lead system byantenna action. Subjected to RF frequencies, the lead itself can exhibitcomplex transmission line behavior.

At the frequencies of interest in MRI, RF energy can be absorbed andconverted to heat. The power deposited by RF pulses during MRI iscomplex and is dependent upon the power [Specific Absorption Rate (SAR)Level] and duration of the RF pulse, the transmitted frequency, thenumber of RF pulses applied per unit time, and the type of configurationof the RF transmitter coil used. The amount of heating also depends uponthe volume of tissue imaged, the electrical resistivity of tissue andthe configuration of the anatomical region imaged. There are also anumber of other variables that depend on the placement in the human bodyof the AIMD and the length and trajectory of its associated lead(s). Forexample, it will make a difference how much EMF is induced into apacemaker lead system as to whether it is a left or right pectoralimplant. In addition, the routing of the lead and the lead length arealso very critical as to the amount of induced current and heating thatcan occur. Also, distal tip design is very important as it can heat updue to MRI RF induced energy.

The cause of heating in an MRI environment is twofold: (a) RF fieldcoupling to the lead can occur which induces significant local heating;and (b) currents induced between the distal tip and tissue during MRI RFpulse transmission sequences can cause local Ohms Law (resistive)heating in tissue next to the distal tip electrode of the implantedlead. The RF field of an MRI scanner can produce enough energy to induceRF voltages in an implanted lead and resulting currents sufficient todamage some of the adjacent myocardial tissue. Tissue ablation(destruction resulting in scars) has also been observed. The effects ofthis heating are not readily detectable by monitoring during the MRI.Indications that heating has occurred includes an increase in pacingthreshold, venous ablation, larynx or esophageal ablation, myocardialperforation and lead penetration, or even arrhythmias caused by scartissue. Such long-term heating effects of MRI have not been well studiedyet for all types of AIMD lead geometries. There can also be localizedheating problems associated with various types of electrodes in additionto tip electrodes. This includes ring electrodes or pad electrodes. Ringelectrodes are commonly used with a wide variety of implanted devicesincluding cardiac pacemakers, and neurostimulators, and the like. Padelectrodes are very common in neurostimulator applications. For example,spinal cord stimulators or deep brain stimulators can include at leastten pad electrodes to make contact with nerve tissue. A good example ofthis also occurs in a cochlear implant. In a typical cochlear implantthere are sixteen pad electrodes placed up into the cochlea. Several ofthese pad electrodes make contact with auditory nerves.

Although there are a number of studies that have shown that MRI patientswith active implantable medical devices, such as cardiac pacemakers, canbe at risk for potential hazardous effects, there are a number ofreports in the literature that MRI can be safe for imaging of pacemakerpatients when a number of precautions are taken (only when an MRI isthought to be an absolute diagnostic necessity). While these anecdotalreports are of interest, they are certainly not scientificallyconvincing that all MRI can be safe. For example, just variations in thepacemaker lead length and implant trajectory can significantly affecthow much heat is generated. A paper entitled, HEATING AROUNDINTRAVASCULAR GUIDEWIRES BY RESONATING RF WAVES by Konings, et al.,journal of Magnetic Resonance Imaging, Issue 12:79-85 (2000), does anexcellent job of explaining how the RF fields from MRI scanners cancouple into implanted leads. The paper includes both a theoreticalapproach and actual temperature measurements. In a worst-case, theymeasured temperature rises of up to 74 degrees C. after 30 seconds ofscanning exposure. The content of this paper is fully incorporatedherein by this reference.

The effect of an MRI system on the function of pacemakers, ICDs,neurostimulators and the like, depends on various factors, including thestrength of the static magnetic field, the pulse sequence, the strengthof RF field, the anatomic region being imaged, and many other factors.Further complicating this is the fact that each patient's condition andphysiology is different, and each lead implant has a different lengthand/or implant trajectory in body tissues. Most experts still concludethat MRI for the pacemaker patient should not be considered safe.

It is well known that many of the undesirable effects in an implantedlead system from MRI and other medical diagnostic procedures are relatedto undesirable induced EMFs in the lead system and/or RF currents in itsdistal tip (or ring) electrodes. This can lead to overheating of bodytissue at or adjacent to the distal tip.

Distal tip electrodes can be unipolar, bipolar and the like. It is veryimportant that excessive current not flow at the interface between thelead distal tip electrode and body tissue. In a typical cardiacpacemaker, for example, the distal tip electrode can be passive or of ascrew-in helix type as will be more fully described. In any event, it isvery important that excessive RF current not flow at this junctionbetween the distal tip electrode and for example, myocardial or nervetissue. Excessive current at the distal electrode to tissue interfacecan cause excessive heating of said tissue to the point of tissueablation or even tissue perforation, which can be life threatening forcardiac patients. For neurostimulator patients, such as deep brainstimulator patients, thermal injury can cause coma, permanent disabilityor can even be life-threatening. Similar issues exist for spinal cordstimulator patients, cochlear implant patients and the like.

Interestingly, the inventors performed an experiment in an MRI scannerwith a human body gel-filled phantom. In the phantom, placed in ananatomic position, was an operating pacemaker and a lead. This wasduring evaluation of the efficacy of bandstop filters at or near thedistal tip electrode for preventing the distal tip electrode fromoverheating. Bandstop filters for this purpose are more thoroughlydescribed in U.S. Pat. No. 7,363,090, the content of which is fullyincorporated herein by this reference. During the experiments, there wasa control lead that had no bandstop filter. During a particularly RFintense scanning sequence, Luxtron probes measured a distal helix tipelectrode temperature rise of 30° C. Of course, the 30° C. temperaturerise in a patient would be very alarming as it can lead to pacingcapture threshold changes or even complete loss capture due to scartissue formation. An identical lead with the bandstop filter in placeonly had a temperature rise of 3° C. This was a remarkable validation ofthe efficacy of bandstop filters for implantable electrodes. However,something very interesting happened when we disconnected the pacemaker.We disconnected the pacemaker and put a silicone lead cap over theproximal end of the lead. Again, we put the gel phantom back inside theMR scanner and this time we measured an 11° C. temperature rise on thelead with the bandstop filter. This was proof positive that the housingof the AIMD acts as part of the system. The prior art feedthroughcapacitor created a fairly low impedance at the input to the pacemakerand thereby drew RF energy out of the lead and diverted it to thehousing of the pacemaker. It has recently been discovered that theimpedance, and in particular, the ESR of these capacitors, is veryimportant so that maximal energy can be pulled from the lead anddiverted to the pacemaker housing while at the same time, not undulyoverheating the feedthrough capacitor.

Accordingly, there is a need for novel low ESR diverting capacitors andcircuits which are frequency selective and are constructed of passivecomponents for implantable leads and/or leadwires. Further, there is aneed for very low ESR diverter element capacitor(s) which are designedto decouple a maximum amount of induced RF energy from an implanted leadto an AIMD housing while at the same time not overheat. The presentinvention fulfills these needs and provides other related advantages.

SUMMARY OF THE INVENTION

An exemplary embodiment of the present invention is a filteredfeedthrough assembly attachable to an opening of a housing of an activeimplantable medical device. The filtered feedthrough assembly comprises:a hermetic feedthrough comprising: (I) a metallic and electricallyconductive ferrule configured to be installed in the opening of thehousing of the active implantable medical device, the ferrule separatinga body fluid side opposite a device side, and the ferrule comprising aferrule opening extending from the body fluid side to the device side;(ii) an insulator disposed at least partially within the ferruleopening; (iii) a first hermetic seal disposed between the insulator andthe ferrule opening hermetically sealing the insulator to the ferrule;(iv) at least one passageway disposed through the insulator extendingfrom the body fluid side to the device side; (v) a conductive pathwaydisposed within the at least one passageway, the conductive pathwayhermetically sealed to the at least one passageway. At least one filtercapacitor is disposed on the device side, comprising: (i) at least oneactive electrode plate and at least one ground electrode plate disposedwithin a capacitor dielectric body in spaced and interleaved relationwith each other; (ii) a capacitor active metallization attached to thecapacitor dielectric body and electrically connected to the at least oneactive electrode plate; (iii) a ground capacitor metallization attachedto the capacitor dielectric body and electrically connected to the atleast one ground electrode plate; (iv) wherein the at least one filtercapacitor is the first filter capacitor electrically connected to theconductive pathway coming from the body fluid side into the device side;(v) wherein the capacitor dielectric body (148) has a dielectricconstant k that is greater than 0 and less than 1,000. An activeelectrical connection electrically connects the conductive pathway tothe capacitor active metallization, and a ground electrical connectionelectrically connects the ground capacitor metallization to the ferrule.Further embodiments of the invention are now discussed herein.

As best shown in FIGS. 63-64C and 65A-65R, the at least one filtercapacitor may be a flat-through filter capacitor.

Furthermore, the flat-through filter capacitor may be disposed at leastpartially over the insulator in a tombstone mounting position, whereinthe at least one active electrode plate and the at least one groundelectrode plate are disposed perpendicular in relation to an outsidesurface of the ferrule on the device side, best shown in FIGS. 65A-65R.

The ground capacitor metallization may be disposed at an edge of theflat-through filter capacitor as shown in FIG. 65A. The groundelectrical connection may comprise a conductive wire gold brazed orwelded to the ferrule. The ground electrical connection may comprise aconductive material electrically connecting the ground capacitormetallization to the conductive wire gold brazed or welded to theferrule. The ground electrical connection may comprise a gold pocket-paddisposed within a pocket formed in the outside surface of the ferrule.The ground electrical connection may comprise a conductive materialelectrically connecting the ground capacitor metallization to the goldpocket-pad. The ground electrical connection may comprise a conductivematerial electrically connecting the ground capacitor metallization to agold braze forming the first hermetic seal. The ground electricalconnection may comprise a metallization layer disposed on the outsidesurface of the ferrule which is overlaid by an electrically conductiveadhesive. The ground electrical connection may comprise a conductivematerial electrically connecting the ground capacitor metallization tothe electrically conductive adhesive.

The ground capacitor metallization may be disposed in a middle of theflat-through filter capacitor as best shown in FIG. 65E. The groundelectrical connection may comprise a conductive wire gold brazed orwelded to a peninsula or a bridge extending into the ferrule opening ofthe ferrule. The ground electrical connection may comprise a conductivematerial electrically connecting the ground capacitor metallization tothe conductive wire gold brazed or welded to the ferrule. The groundelectrical connection may comprise a gold pocket-pad disposed within apocket formed in the outside surface of a peninsula or a bridgeextending into the ferrule opening of the ferrule. The ground electricalconnection may comprise a conductive material electrically connectingthe ground capacitor metallization to the gold pocket-pad.

As best shown in FIG. 65I, the ground capacitor metallization maycomprise a first ground capacitor metallization disposed at an edge ofthe flat-through filter capacitor and a second ground capacitormetallization disposed in a middle of the flat-through capacitor,wherein the second ground metallization is electrically connected to theferrule at a peninsula or a bridge extending into the ferrule opening ofthe ferrule.

The flat-through filter capacitor may be disposed on a circuit board,the circuit board comprising at least one ground plate disposed in or onthe circuit board, and wherein the at least one ground plate iselectrically connected to the ground capacitor metallization and to theferrule.

The at least one filter capacitor may be an X2Y attenuator filtercapacitor.

As best shown in FIGS. 70C and 70D, the at least one filter capacitormay be disposed at least partially over the insulator in a tombstonemounting position, wherein the at least one active electrode plate andthe at least one ground electrode plate are disposed perpendicular inrelation to an outside surface of the ferrule on the device side. Theground electrical connection may comprise a conductive materialelectrically connecting the ground capacitor metallization to a goldbraze forming the first hermetic seal.

The X2Y attenuator filter capacitor may be disposed on a circuit board,the circuit board comprising at least one ground plate disposed in or onthe circuit board, and wherein the at least one ground plate iselectrically connected to the ground capacitor metallization and to theferrule.

The first hermetic seal may comprise a first gold braze. The conductivepathway may comprise a leadwire, the leadwire hermetically sealing theat least one passageway by a second gold braze.

The conductive pathway may comprise a platinum fill co-fired with theinsulator or the conductive pathway may comprise a ceramic reinforcedmetal composite co-fired with the insulator.

As best shown in FIGS. 70C and 70D, another embodiment of the presentinvention is a filtered feedthrough assembly attachable to an opening ofa housing of an active implantable medical device, the filteredfeedthrough assembly comprising: a) a hermetic feedthrough, comprising:(i) a metallic and electrically conductive ferrule configured to beinstalled in the opening of the housing of the active implantablemedical device, the ferrule separating a body fluid side opposite adevice side, and the ferrule comprising a ferrule opening extending fromthe body fluid side to the device side; (ii) an insulator disposed atleast partially within the ferrule opening; (iii) a first hermetic sealdisposed between the insulator and the ferrule opening hermeticallysealing the insulator to the ferrule; (iv) a first and a secondpassageway disposed through the insulator extending from the body fluidside to the device side; (v) a first and a second conductive pathwaydisposed respectively within the first and the second passageway, theconductive pathways hermetically sealed to their respective passageways;b) an X2Y attenuator filter capacitor disposed on the device side,comprising: (i) at least a first and a second active electrode plate andat least one ground electrode plate (146) disposed within a capacitordielectric body in spaced and interleaved relation with each other; (ii)a first and a second capacitor active metallization attached to thecapacitor dielectric body and electrically connected respectively to thefirst and the second active electrode plates; (iii) a ground capacitormetallization attached to the capacitor dielectric body and electricallyconnected to the at least one ground electrode plate; (iv) wherein theX2Y attenuator filter capacitor is the first filter capacitorelectrically connected to the conductive pathways coming from the bodyfluid side into the device side; (v) wherein the X2Y attenuator filtercapacitor is disposed at least partially over the insulator in atombstone mounting position, wherein the at least the first and thesecond active electrode plate and the at least one ground electrodeplate are disposed perpendicular in relation to an outside surface ofthe ferrule on the device side; c) a first active electrical connectionelectrically connecting the first conductive pathway to the firstcapacitor active metallization; d) a second active electrical connectionelectrically connecting the second conductive pathway to the secondcapacitor active metallization; and e) a ground electrical connectionelectrically connecting the ground capacitor metallization to theferrule.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, taken inconjunction with the accompanying drawings which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a wire-formed diagram of a generic human body showing a numberof exemplary implanted medical devices;

FIG. 2 is a pictorial view of an AIMD patient who is about to be placedinto an MRI scanner;

FIG. 3 shows a side view of the patient within the scanner showing anintense RF field impinging on the implanted medical device and itsassociated lead;

FIG. 4 is a top view of the patient in the MRI scanner showing onelocation of the AIMD and its associated lead;

FIG. 5 is a line drawing of a human heart with cardiac pacemaker dualchamber bipolar leads shown in the right ventricle and the right atrium;

FIG. 6 illustrates a dual chamber cardiac pacemaker with its associatedleads and electrodes implanted into a human heart;

FIG. 7 is an isometric view illustrating the rectangular feedthroughcapacitor mounted to a hermetic terminal;

FIG. 8 is an enlarged cross-sectional view taken generally along theline 8-8 of FIG. 7;

FIG. 9 is an isometric view of a round hermetic terminal showing a quadpolar RF diverter feedthrough capacitor;

FIG. 10 is an enlarged cross-sectional view taken generally along theline 10-10 from FIG. 9;

FIG. 11 is an electrical schematic diagram of the quad polar feedthroughcapacitor of FIGS. 7-10;

FIG. 12 is a cross-sectional view of an embodiment of a hermeticterminal subassembly installed in a housing of an AIMD;

FIG. 13 is a cross-sectional view of another embodiment of a hermeticterminal subassembly now showing a capacitor with a filled and abore-coated via;

FIG. 14 is an isometric view of a monolithic multi-layer ceramiccapacitor (MLCC) chip capacitor;

FIG. 15 is a cross-sectional view of the monolithic ceramic capacitor,taken along the line 15-15 of FIG. 14;

FIG. 16 is an electrical schematic diagram of an ideal MLCC chipcapacitor as illustrated in FIGS. 14 and 15;

FIG. 17 is an isometric view of a flat-through three-terminal capacitor;

FIG. 18 illustrates the internal electrode plates of the flat-throughcapacitor of FIG. 17;

FIG. 18A is the electrical schematic of FIGS. 17 and 18;

FIG. 19 is an isometric exploded view of a multi-lead hermeticfeedthrough with substrate mounted MLCC chip capacitors showing use of asubstrate between the feedthrough and the filter support assembly;

FIG. 19A is the electrical schematic of FIG. 19;

FIG. 20 illustrates a cross-sectional view of an MLCC chip capacitormounted to separate circuit traces;

FIG. 21 is a schematic representation explaining the elements that arecomponents of the FIG. 20 capacitor's equivalent series resistance(ESR);

FIG. 22 is an equation that relates the capacitance with the capacitor'sactive area, dielectric constant, number of electrode plates anddielectric thickness;

FIG. 23 shows the difference between an ideal capacitor and a realcapacitor, including dielectric loss tangent and dissipation factor;

FIG. 24 gives the formulas for capacitive reactance, dissipation factor,equivalent series resistance (ESR) and dielectric loss tangent;

FIG. 25 is an equivalent circuit model for a real capacitor;

FIG. 26 is a schematic illustrating a simplified model for capacitorESR;

FIG. 27 is a graph illustrating capacitor dielectric loss versusfrequency;

FIG. 28 is a graph illustrating normalized curves which show thecapacitor equivalent series resistance (ESR) on the y axis, versusfrequency on the x axis;

FIG. 29 illustrates the reactance and real losses of a 2,000-picofaradX7R feedthrough capacitor;

FIG. 30 illustrates the reactance and real losses of a 2,000-picofaradC0G (NP0) capacitor;

FIG. 31 is a graph illustrating capacitor equivalent series resistanceversus frequency as illustrated in a sweep from an Agilent E4991Amaterials analyzer;

FIG. 32 is a cross-sectional view of a low k MLCC chip capacitor with anincreased number of electrode plates to minimize ESR;

FIG. 33 is an equation showing that the total high frequency electroderesistive losses drop in accordance with the parallel plate formula forcapacitor electrode plates;

FIG. 34 is a cross-sectional view of a quad polar feedthrough capacitorsimilar to FIGS. 9 and 10 except that it is low ESR and designed formaximal heat flow;

FIG. 35 is a partial cross-section taken from section 35-35 from FIG. 34illustrating dual electrode plates to minimize capacitor ESR andmaximize heat flow out of the capacitor;

FIG. 36 is similar to FIG. 35 except that just the ground electrodeplates have been doubled;

FIG. 37 illustrates a family of lowpass filters indicating the presentinvention can be anything from a simple diverter capacitor 140 to ann-element lowpass filter;

FIG. 38 illustrates a feedthrough diverter capacitor, a bandstop filterand an L-C trap;

FIG. 39 illustrates a cardiac pacemaker with a diverter feedthroughcapacitor and also a circuit board mounted chip capacitor filter whichforms a composite filter and also spreads out heat generation;

FIG. 39A illustrates the electrical schematic of FIG. 39;

FIG. 39B is a perspective view showing the capacitor mounted to aflexible connection;

FIG. 39C illustrates the electrical schematic of FIG. 39B;

FIG. 40 is a fragmented perspective view of an EMI shield conduitmounted to a circuit board having multiple MLCC chip capacitors;

FIG. 41 is a cross-sectional view of a flex cable embodying the presentinvention;

FIG. 42 is a sectional view taken along line 42-42 of FIG. 41;

FIG. 43 is a sectional view taken along the line 43-43 of FIG. 41,illustrating an alternative to the internal circuit traces disclosedwith respect to FIG. 42;

FIG. 44 is a sectional view taken along line 44-44 of FIG. 41,illustrating one of a pair of coaxially surrounding shields disposedabout the circuit trace;

FIG. 45 is an isometric view of the flex cable of FIG. 41 connected to acircuit board or substrate having a flat-through capacitor;

FIG. 46 is the top view of the flat-through capacitor from FIG. 45;

FIG. 47 illustrates the active electrode plates of the flat-throughcapacitor of FIGS. 45 and 46;

FIG. 48 illustrates the ground electrode plate of the flat-throughcapacitor of FIGS. 45 and 46;

FIG. 49 illustrates a family of lowpass filters, which is very similarto the family of lowpass filters described in FIG. 37;

FIG. 49A is similar to FIG. 49 now showing the attenuation curve for afeedthrough capacitor with chip capacitor;

FIG. 50 illustrates that the high energy dissipating low ESR capacitorcan be used in combination with other circuits;

FIG. 51 shows an isometric view of an MLCC chip capacitor that issimilar in its exterior appearance to the prior art MLCC chip capacitorpreviously described in FIGS. 14 and 15;

FIG. 52 is a cross-sectional view taken along lines 52-52 of FIG. 51;

FIG. 53 is the electrical schematic representation of FIGS. 51 and 52;

FIG. 54 is an isometric view of a bipolar hermetic seal having a ferruleand two leads passing through the conductive ferrule in insulativerelationship;

FIG. 55 is the electrical schematic representation of FIG. 54;

FIG. 56 is similar to FIG. 6 showing a breakaway cross-section of atypical AIMD with novel capacitors mounted to an internally disposedcircuit board;

FIG. 56A is the electrical schematic of FIG. 56;

FIG. 57 is very similar to FIG. 56 except that a diode array has beenadded;

FIG. 58 is the electrical schematic representation of FIG. 57;

FIG. 59 is very similar to FIG. 58 except the high voltage protectiondiode array is shown on the other side of the low ESR capacitors;

FIG. 60 is an electrical schematic of a back-to-back diode placed inseries taken from lines 60-60 of FIG. 59;

FIG. 61 is very similar to FIG. 56 except that the RF grounding straphas been replaced with a simple leadwire connection;

FIG. 62 is very similar to FIG. 61 now with the grounding leadwirerouted directly to the ferrule of the hermetic terminal subassembly;

FIG. 63 is very similar to prior art FIG. 17 that illustrated aflat-through type of feedthrough capacitor;

FIG. 64 is very similar to prior art FIG. 18 that illustrated theelectrode plates of the flat-through type of feedthrough capacitor;

FIG. 64A is the electrical schematic for FIGS. 63 and 64;

FIG. 64B is a top view of an embodiment of the flat-through capacitor ofFIG. 63 now mounted upon a circuit board;

FIG. 64C is a cross-sectional view taken along lines 64C-64C from thestructure of FIG. 64B;

FIG. 64D is an isometric view of a quad polar flat-through filtercapacitor;

FIG. 64E is a sectional view taken along lines 64E-64E from thestructure of FIG. 64D;

FIG. 64F is the electrical schematic for FIGS. 64D and 64E;

FIG. 65A is a top view of an embodiment of the quad polar flat-throughfilter capacitor of FIG. 64D now mounted above a ferrule and insulatorin a tombstone mounting position;

FIG. 65B is a cross-sectional view taken along lines 65B-65B from thestructure of FIG. 65A;

FIG. 65C is an isometric view of an internally grounded quad polarflat-through capacitor;

FIG. 65D is a sectional view taken along lines 65D-65D from thestructure of FIG. 65C;

FIG. 65E is a top of view of an embodiment of the internally groundedquad polar flat-through capacitor of FIG. 65C now mounted above aferrule and insulator in a tombstone mounting position;

FIG. 65F is a cross-sectional view taken along lines 65F-65F from thestructure of FIG. 65E;

FIG. 65G is an isometric view of a hybrid quad polar flat-throughcapacitor;

FIG. 65H is a sectional view taken along lines 65H-65H from thestructure of FIG. 65G;

FIG. 65I is a top view of an embodiment of the hybrid quad polarflat-through capacitor of FIG. 65G now mounted above a ferrule andinsulator in a tombstone mounting position;

FIG. 65J is a cross-sectional view taken along lines 65J-65J from thestructure of FIG. 65I;

FIG. 65Ja is an enlarged partial cross-sectional view generally takenfrom section 65Ja-65Ja from FIG. 65J now showing a new embodiment of agrounding structure;

FIG. 65Jb is an enlarged partial cross-sectional view generally takenfrom section 65Jb-65Jb from FIG. 65J now showing a new embodiment of agrounding structure;

FIG. 65Jc is an enlarged partial cross-sectional view generally takenfrom section 65Jc-65Jc from FIG. 65J now showing a new embodiment of agrounding structure;

FIG. 65Jd is an enlarged partial cross-sectional view generally takenfrom section 65Jd-65Jd from FIG. 65J now showing a new embodiment of agrounding structure;

FIG. 65K is a top view of an embodiment of the hybrid quad polarflat-through capacitor of FIG. 65G now mounted above a ferrule andinsulator in a tombstone mounting position;

FIG. 65L is a side view taken along lines 65L-65L from the structure ofFIG. 65K;

FIG. 65M is a side view taken along lines 65M-65M from the structure ofFIG. 65K;

FIG. 65N is a top view of another embodiment of a ferrule and insulatorstructure;

FIG. 65O is an isometric view of a novel flat-through capacitor of thepresent invention;

FIG. 65P is a view similar to that of FIG. 65O now with the dielectricand outside metallizations removed;

FIG. 65Q is a top view of an embodiment of a flat-through capacitor ofFIG. 65O now mounted above a ferrule and insulator in a tombstonemounting position;

FIG. 65R is a cross-sectional view taken along lines 65R-65R from thestructure of FIG. 65Q;

FIG. 65S is a cross-sectional view taken along lines 65S-65S from thestructure of FIG. 65Q;

FIG. 65T is a cross-sectional view taken along lines 65T-65T from thestructure of FIG. 65Q;

FIG. 66 is an isometric view of a bipolar X2Y attenuator;

FIG. 67 shows the internal active electrode plates of FIG. 66 now withthe dielectric removed;

FIG. 68 shows the internal ground electrode plates of FIG. 66 now withthe dielectric removed;

FIG. 69 shows how the active and ground electrode plates of FIG. 66 nestparallel to one another with the dielectric removed;

FIG. 69B is another view of a similar bipolar X2Y attenuator now havinga grounding metallization stripe over the entire outside surface;

FIG. 69C is a sectional view taken along lines 69C-69C from thestructure of FIG. 69B;

FIG. 69D is the electrical schematic of the X2Y attenuator of FIGS.66-69C;

FIG. 70A is a top view of another embodiment of the X2Y attenuator inFIGS. 66-69D now disposed on a circuit board disposed over an insulatorand ferrule;

FIG. 70B is a cross-sectional view taken along lines 70B-70B from thestructure of FIG. 70A;

FIG. 70C is a top view of another embodiment of an X2Y attenuatordisposed in a tombstone mounting position over an insulator and aferrule;

FIG. 70D is an enlarged view taken along lines 70D-70D from FIG. 70Cshowing just one of the X2Y attenuators where the active and groundelectrode plates are now visible;

FIG. 71A illustrates an isometric view of a gold pocket-pad electricallyconnected to the ferrule for use with the present invention;

FIG. 71B illustrates the structure of FIG. 71A now with a capacitor ofthe present invention installed;

FIG. 71C is a view similar to FIG. 71B now illustrating how thecapacitor can be oversized such at least one of its ends can extend pastthe edge of the ferrule;

FIG. 72A is a view similar to FIG. 71A now illustrating a novel goldpocket-pad extending along the long side of the ferrule therebyfacilitating attachment of a larger capacitor;

FIG. 72B is a view similar to FIG. 72A now illustrating the capacitorattached;

FIG. 72C is a view similar to FIG. 72B now illustrating the capacitormetallization being grounded to the gold braze of the insulator;

FIG. 73 is a cross-sectional view taken along lines 73-73 of FIG. 72B;

FIG. 74A is a perspective view of an internally grounded feedthroughcapacitor of the present invention before it is installed onto theferrule;

FIG. 74B is a view similar to FIG. 74A now showing the electrode platestack up;

FIG. 74C is a view similar to FIGS. 74A and 74B now showing theinternally grounded feedthrough capacitor installed;

FIG. 75 is a top view illustrating how a rectangular capacitor canoverhang the ferrule;

FIG. 76 is a cross-sectional side view taken along lines 76-76 from FIG.75;

FIG. 77 is a cross-sectional side view of another embodiment of thepresent invention utilizing a cermet disposed within a via hole in theinsulator along with an internally grounded capacitor utilizing the goldpocket-pad for the oxide-resistant connection to the ferrule;

FIG. 78 is a cross-sectional view very similar to FIG. 77 now showingthe use of an anisotropic film for making electrical connection on thedevice side;

FIG. 79 is a cross-sectional side view illustrating a variety of filledvias utilizing co-fired fills that can be used with the presentinvention;

FIG. 80 is a top view of another embodiment of a filtered feedthrough ofthe present invention;

FIG. 81 is a sectional top view taken along lines 81-81 of FIG. 82;

FIG. 82 is a cross-sectional side view taken along lines 82-82 of FIG.80;

FIG. 83 is a cross-sectional side view taken along lines 83-83 of FIG.80;

FIG. 84 is a cross-sectional side view illustrating the use of a metaladdition for an oxide resistant attachment;

FIG. 85 is cross-sectional side view of another embodiment of thepresent invention utilizing a two-part pin extending through theinsulator;

FIG. 86 is a flow chart including a novel pressing step for a co-firedinsulator assembly having a conductive composite sintered paste via forachieving improved hermeticity and durability;

FIG. 87 is a cross-sectional view of the insulator assembly in the greenstate of FIG. 87 before pressing; and

FIG. 88 is a cross-sectional view of the structure of FIG. 88 after thepressing step resulting in a mixing zone between the differentstructures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates various types of active implantable medical devices(AIMD) referred to generally by the reference numeral 100 that arecurrently in use. FIG. 1 is a wire formed diagram of a generic humanbody showing a number of exemplary implanted medical devices. Numericaldesignation 100A is a family of implantable hearing devices which caninclude the group of cochlear implants, piezoelectric sound bridgetransducers and the like. Numerical designation 100B includes an entirevariety of neurostimulators and brain stimulators. Neurostimulators areused to stimulate the Vagus nerve, for example, to treat epilepsy,obesity and depression. Brain stimulators are similar to apacemaker-like device and include electrodes implanted deep into thebrain for sensing, for example, the onset of a seizure and alsoproviding electrical stimulation to brain tissue to prevent a seizurefrom actually happening. Numerical designation 100C shows a cardiacpacemaker which is well-known in the art. Numerical designation 100Dincludes the family of left ventricular assist devices (LVAD's), andartificial hearts, including the artificial heart known as the Abiocor.Numerical designation 100E includes an entire family of drug pumps whichcan be used for dispensing of insulin, chemotherapy drugs, painmedications and the like. Drug pumps are evolving from passive devicesto ones that have sensors and closed loop systems. For example, insulinpumps provide real time monitoring of blood sugar levels and candispense insulin in accordance with the insulin levels sensed. Suchactive pump devices tend to be more sensitive to EMI than passive pumpsthat have no sense circuitry or externally implanted leadwires. 100Fincludes a variety of implantable bone growth stimulators for rapidhealing of fractures. Numerical designation 100G includes urinaryincontinence devices. Numerical designation 100H includes the family ofpain relief spinal cord stimulators and anti-tremor stimulators.Numerical designation 100H includes an entire family of other types ofneurostimulators used to block pain. Numerical designation 100I includesa family of implantable cardioverter defibrillator (ICD) devices andalso includes the family of congestive heart failure devices (CHF), alsoknown in the art as cardio resynchronization therapy devices or CRTdevices. Numerical designation 100J illustrates an externally worn pack.Exemplary externally worn packs include external insulin pumps, externaldrug pumps, external neurostimulators and even ventricular assistdevices.

Referring to U.S. Pat. No. 7,844,319, the content of which is fullyincorporated herein by this reference, paragraphs 79 through 82 describemetallic structures, particularly leads, that when placed in MRIscanners, can pick up high electrical fields, which results in localtissue heating. Such local heating tends to be most concentrated at theends of the electrical structure (either at the proximal or distal leadends), which is a safety issue. Such heating safety issues can beaddressed using the disclosed systems and methods of the presentinvention. A significant concern is that the distal electrodes, whichare in contact with body tissue, can cause local tissue burns, and mayeven permanently damage tissue at the burn site.

As defined herein, an active implantable medical device (AIMD) includesany device or system that is designed to be totally or partiallyintroduced or implanted within a human body for diagnostic ortherapeutic purposes and includes at least one electronic circuitry.AIMDs may have primary or secondary (rechargeable) batteries as theirenergy sources. AIMDs may also harvest energy from the body eitherthrough mechanical motion, body motion, thermal energy, chemical orbiochemical battery cell type effects or externally induced ultrasonicenergy. An AIMD may also contain a resonant circuit whereby it capturesenergy from external pulsing electromagnetic field. An example of thisis what is known in the industry as the Bion®. In general, AIMDs areconnected to either a leadwire or are directly connected to electrodeswithout a leadwire wherein, these electrodes are contactable tobiological cells. AIMD electrodes may be used for therapy delivery,sensing of biological signals or both. AIMDs may also be integrated withfiber optic cables and receive their power or signals optically whereinthere is an optical converter which may convert the optical signals toeither digital signals or to power.

A subclass of AIMDs is known as cardiac implantable electronic devices(CIEDs). CIEDs include all types of pacemakers, implantable cardioverterdefibrillators, implantable loop recorders, subcutaneous ICDs and thelike. Another subclass of AIMDs includes all types of neurostimulators,including, but not limited to spinal cord stimulators, deep brainstimulators, urinary incontinence stimulators and the like. An AIMD mayinclude an external component, such as an RF transmitter, an RFtelemetry device or even a worn wrist watch, which sends signals to animplanted device and its associated electrodes. In other words, theAIMD, as defined herein can have externally worn components in additionto implanted components.

In general, an AIMD usually has a housing, which is generally conductiveand forms an electromagnetic shield (Faraday cage) thereby protectingone or more internal electronic circuits from undesirableelectromagnetic interference (EMI). As used herein, the body fluid sideof an AIMD is defined as the exterior or the outside of the AIMDhousing. Any components residing on the outside of an AIMD housing areon the body fluid side of the AIMD (e.g., header block, therapy deliveryleads). The device side of the AMID, also known as an inboard side, isdefined as the interior of or the inside the AIMD housing. Anycomponents or electronic circuits residing within an AIMD housing are onthe device side of the AIMD (e.g., AIMD active electronic circuit board,the battery and/or capacitor).

It is understood by those skilled in the art that the use of the termbody fluid side and device side can be applied to the filter feedthroughassembly before it is installed into the housing of the AIMD. It isknown and shown throughout this specification that the filter capacitoris generally installed on the device side of the feedthrough, however,can alternatively be installed on the body fluid side of thefeedthrough.

As used herein, the terms insulator substrate and insulator body aresynonymous and can be used interchangeably. Furthermore, the termsdielectric, dielectric substrate and dielectric body are synonymous andcan be used interchangeably.

As used herein, the word “adjacent” means either adjoining a structure,attached to an adjacent structure, or near an adjacent structure. Forexample, FIG. 78 describes a capacitor 140 that is mounted adjacent tothe ferrule 134 or the insulator 156. Mounted adjacent to the ferrule,in this context, can mean mounted right on the ferrule, mounted right onthe insulator or spaced by an air gap or spaced by some sort of anadhesive washer or the like. In this context, adjacent has a broadmeaning, simply meaning that the capacitor has to be near or on one ofthe ferrule or the insulator. Throughout the specification, the word“adjacent” means next to, adjoining, contiguous, on, neighboring,approximate or even slightly spaced away from (such as lying near).

As used herein, the conductive composite paste fill takes on the shapeof the insulator passageway within which it is disposed. Post sintering,the paste fill becomes a conductive composite sintered paste fill whichforms a solid conductive structure. The conductive composite sinteredpaste fill conformally forms a hermetic seal within the insulatorpassageway, thereby separating the body fluid side of the hermetic sealfrom the device side of the hermetic seal. To one skilled in the art, itis understood that the conductive composite paste fill before sinteringdoes not have a defined shape, but rather is a thick, soft, moist pastefilling an insulator passageway. After sintering, the paste takes on adefined shape conformal with that of the insulator passageway.

As used herein, the lead means an implanted lead, including itsconductors and electrodes, the electrodes being contactable with bodytissue. In general, for an AIMD, the term lead means the lead that isoutside of the AIMD housing and is implanted or directed into bodytissues. The term leadwire as used herein refers to the wiring orcircuit traces that are generally inside of the active implantablemedical device (AIMD) and are not exposed directly to body fluids.

FIG. 2 illustrates an AIMD patient 102 about to be conveyored into anMRI scanner 104. Imaging processing equipment is shown as 106.

FIG. 3 is a side view showing the AIMD patient 102 within the bore of anMRI scanner 104. An intense RF-pulse field 108 is generated by thescanner's bird cage coil. As can be seen, this RF field is impinging onboth the implanted cardiac pacemaker 100C and its associated leads 110.

FIG. 4 is a top view of the AIMD patient 102 inside the bore of the MRIscanner 104. As can be seen, the implanted cardiac pacemaker 100C is ina left pectoral pocket with the leads 110 routed transvenously into theinterior chambers of the human heart.

FIG. 5 is a line drawing of a human heart 112 and an implantable cardiacpacemaker 100C having dual chamber bipolar leads 110 shown in the rightventricle 114 and the right atrium 116.

Referring once again to FIG. 5, as previously mentioned, it is veryimportant that the leads 110 of the implantable cardiac pacemaker 112 donot overheat during MRI procedures particularly at or near the distaltip electrodes 118 a, 118 b and ring electrodes 120 a, 120 b. If eitheror both the distal tip electrodes 118 a, 118 b and ring electrodes 120a, 120 b become overgrown by body tissue, excessive overheating cancause scarring, burning or necrosis of the heart tissue. This can resultin loss of capture (loss of pacing pulses) which can be life-threateningfor a pacemaker dependent patient.

FIG. 6 is similar to FIG. 2 taken from U.S. Pat. No. 10,350,421, thecontent of which is fully incorporated herein by this reference. FIG. 6illustrates a dual chamber implantable cardiac pacemaker 100C with itsbipolar leads 110, 110′. The distal tip electrodes 118 a and 118 b anddistal ring electrodes 120 a and 120 b of the bipolar leads 110, 110′are shown routed to a human heart. During an MRI scan, the leads 110,110′ are exposed to a powerful RF-pulse field which induceselectromagnetic energy on the leads. As the leads 110, 110′ areelectrically connected to such electronic circuitry through the ISOStandard IS-1 or DF-1 connectors 126 a, 126 b, 128 a, 128 b of theheader block 138, the electromagnetic energy induced in the leads 110,110′ can undesirably couple to sensitive electronic circuitry inside ofthe hermetically sealed pacemaker housing 124, thereby potentiallycausing dangerous AIMD malfunction. The header block 138 electricallyconnects leads 110, 110′ to the AIMD circuit board 130 by way of theleadwires 136 a through 136 d of the hermetic feedthrough 132. Thehermetic feedthrough 132 is shown with a metal ferrule 134, which isgenerally laser welded into the AIMD housing 124 of the cardiacpacemaker 100C. Leadwires 136 a through 136 d extend through theinsulator hermetically sealed to the ferrule 134 of the hermeticfeedthrough 132.

Referring once again to FIG. 6, illustrated is a hermetic feedthrough132, which is typically laser welded into an opening 123 of the titaniumhousing 124 of the implantable cardiac pacemaker 100C, therebyhermetically sealing the pulse generator of the implantable cardiacpacemaker 100C. The hermetic seal of the pulse generator of theimplantable cardiac pacemaker 100C keeps body fluids from getting intothe inside of the pacemaker housing 124. The hermetic feedthrough 132typically comprises an electrically conductive ferrule 134 comprising aferrule opening 131 (not labelled) extending to a ferrule body fluidside opposite a ferrule device side and an insulator 156 residing in theferrule opening wherein a gold braze hermetically seals the insulator tothe ferrule.

FIG. 6 illustrates feedthrough conductive pathways 129 (not labelled)comprising leadwires 136 a through 136 d passing through an insulatorpassageway 149 (not labelled) in non-conductive relation with theferrule 134 of the hermetic feedthrough 132, the leadwires 136 a through136 d extending to a body fluid side and a device side of theimplantable cardiac pacemaker 100C. The hermetic feedthrough 132 of theimplantable cardiac pacemaker 100C may comprise a glass, aglass-ceramic, or a ceramic insulator 156. The hermetic feedthroughfurther comprises a leak rate no greater than 1×10⁻⁷ std cc He/sec. Asillustrated in FIG. 6, the hermetic feedthrough 132 comprises afeedthrough filter capacitor 140, which is mounted adjacent to one ofthe ferrule 134, the insulator 156 or both the ferrule and the insulatorof the hermetic feedthrough 132. An embodiment of an exemplary hermeticfeedthrough 132 comprises an alumina insulator 156 gold brazed to atitanium ferrule 134, the insulator comprising at least one insulatorpassageway 149 disposed through the insulator 156. The at least oneinsulator passageway 149 extends to a body fluid side and to a deviceside of the insulator 156. The at least one insulator passageway 149comprises a feedthrough conductive pathway 129 disposed therewithin, thefeedthrough conductive pathway 129 being hermetically sealed to the atleast one insulator passageway. The feedthrough conductive pathway 129comprises an electrical conductor. The electrical conductor of thehermetic feedthrough 132 is selected from the group consisting of aleadwire, a lead wire, a terminal pin, a pin, a two-part pin, a leadconductor, a sintered conductive via, a sintered paste-filled via, aco-sintered via, a co-sintered paste-filled via, a co-sintered via withone or more metallic inserts, or combinations thereof. FIGS. 7 and 8provide another exemplary hermetic feedthrough embodiment in accordancewith the teachings of FIG. 6.

FIGS. 7 and 8 illustrate an exemplary rectangular quad polar (planararray) feedthrough filter capacitor 140 mounted to the hermeticfeedthrough 132 of a cardiac pacemaker in accordance with U.S. Pat. No.5,333,095 to Stevenson et al., the content of which is fullyincorporated herein by this reference. It is understood that afeedthrough filter capacitor 140 may be mounted adjacent to one of theferrule 134, the insulator 156, or both the ferrule and the insulator ofthe hermetic feedthrough 132. Once a filter capacitor is placed on thehermetic feedthrough 132, then the assembly is considered a filteredfeedthrough 122.

As illustrated in FIGS. 7 and 8, in a typical broadband or lowpass EMIfilter construction, a ceramic feedthrough filter capacitor 140 iselectrically connected to a hermetic feedthrough 132 to suppress anddecouple undesired interference or noise transmission along one or moreterminal pins 142. The feedthrough filter capacitor 140 comprises activeelectrode plates 144 and ground electrode plates 146, which are embeddedin spaced relation within a dielectric body 148. The feedthrough filtercapacitor 140 is typically formed as either a ceramic monolithic or aceramic multi-layered structure. The active electrode plates 144 areelectrically connected to an inner diameter cylindrical surface to anactive capacitor metallization 164 of the feedthrough filter capacitor140 and to the active terminal pins 142 so that the desired electricalsignal or signals may pass along an active conductive path (FIG. 11illustrates the electrical schematic diagram). The ground electrodeplates 146 are electrically coupled to a ground capacitor metallization166 at a sidewall of the dielectric body 148, the ground capacitormetallization in this embodiment being an outer edge metallization ofthe feedthrough filter capacitor 140. The ground capacitor metallization166 is shown electrically connected to a gold pocket-pad 158 of arectangular electrically conductive ferrule 134 using an electricallyconductive material 152. The gold pocket-pad 158 embodiment of FIG. 8 isa part of the gold braze 154 a hermetically sealing the insulator 156 ofthe hermetic feedthrough 132 to the ferrule 134. It is noted that thestructure of the gold pocket-pad 158 may be a separate pocket structurefrom the gold braze hermetically sealing the insulator to the ferrule ormay be a gold pocket-pad area that is a structural extension of the goldbraze hermetically sealing the insulator to the ferrule as shown in FIG.8. As used herein, a gold pocket-pad that is separate from the goldbraze hermetically sealing the insulator to the ferrule and a goldpocket-pad area that is a structural extension of the gold brazehermetically sealing the insulator to the ferrule each provideoxide-resistant electrical attachment to a feedthrough filter capacitor140. In the prior art, without regard to high frequency capacitor ESR,the number and dielectric thickness spacing of the active electrodeplates 144 and the ground electrode plates 146 will vary in accordancewith the capacitance value and the voltage rating of the feedthroughfilter capacitor 140.

In operation, the coaxial feedthrough filter capacitor 140 permitspassage of relatively low frequency electrical signals along theterminal pins 142, while also shielding and decoupling/attenuatingundesired interference signals of typically high frequency to theconductive housing 124. Feedthrough filter capacitors 140 of thisgeneral type are available in unipolar (one), bipolar (two), tripolar(three), quad polar (four), pentapolar (five), hexpolar (6), “n” polarand can be designed to accommodate various terminal pin designconfigurations and/or terminal pin design layouts. Such feedthroughfilter capacitors 140 can further be of various shapes, for example,round, oval, rectangular, discoidal and even custom configurations. Suchfeedthrough filter capacitors 140 are commonly employed in activeimplantable medical devices (AIMD) such as implantable cardiacpacemakers, defibrillators, neurostimuators and the like, wherein theAIMD housing 124 of these AIMDs is constructed from a biocompatiblemetal such as, but not limited to, titanium or a titanium alloy. As aresult, the filter capacitor and hermetic feedthrough prevent entranceof interference signals to the interior of the pacemaker housing 124,wherein such interference signals can otherwise adversely affect thedesired cardiac pacing, defibrillation or neurostimulation function.

As illustrated in FIG. 7, the electrically conductive material 152 (forexample, an electrically conductive polyimide, an electricallyconductive adhesive, an electrically conductive epoxy, an electricallyconductive thermal-setting polymer or a solder) connects the groundcapacitor metallization 166 and the gold pocket-pad area 158. The goldpocket-pad area 158 forms a metallurgical bond with the titanium of theferrule 134 of the hermetic feedthrough 132 and precludes anypossibility of an unstable oxide forming. Gold is a noble metal thatdoes not readily oxidize and remains very stable even at elevatedtemperatures. The novel gold braze structure and constructionmethodology illustrated in FIG. 7 guarantee that the ohmic losses of thefeedthrough filter capacitor 140 will remain very small at allfrequencies. By connecting the ground electrode plates 146 of thefeedthrough filter capacitor 140 to a low resistivity oxide-resistantmaterial such as the gold pocket-pad area 158, one is guaranteed thatthis electrical connection will not substantially contribute to theoverall ESR of the feedthrough filter capacitor 140. Keeping the ESR ofthe feedthrough filter capacitor 140 as low as possible is veryimportant for diverting a high amount of RF current such as is inducedin the AIMD lead system during MRI scanning. One is referred to U.S.Pat. No. 6,765,779 to Stevenson et al. for additional information onelectrically connecting to oxide-resistant materials, the content ofwhich is fully incorporated herein by this reference.

FIG. 8 is a cross-section of feedthrough filter capacitor 140 and thehermetic feedthrough 132 of FIG. 7. One can see that the gold braze 154a that forms the hermetic seal between the alumina insulator 156 and thetitanium ferrule 134 is desirably on the feedthrough capacitor side.This makes it easy to manufacture the gold pocket-pad area 158 forconvenient attachment by the electrically conductive material 152. Inother words, designing the gold pocket-pad area 158 on the same side asthe gold braze 154 a hermetically sealing the insulator 156 to theferrule 134 permits the gold pocket-pad 158 to be co-formed at the sametime as the gold braze 154 a is formed in one manufacturing operation ina gold braze vacuum furnace regardless of whether the gold pocket-padarea is structurally a part of the gold braze hermetic seal or aseparate gold pocket-pad spaced apart from the gold braze hermetic seal.FIG. 8 also illustrates an insulative material 160 (which can be aninsulating washer) disposed between the feedthrough filter capacitor 140and the underlying hermetic feedthrough 132. As illustrated, theinsulator 156 is at least partially disposed within a ferrule opening131. Also shown is an insulator passageway 149 formed in the insulator156 allowing a terminal pin 142 or a leadwire 136 (such as illustratedin FIG. 6) to be hermetically sealed by gold braze 152 b. The terminalpin 142 of FIG. 8 extends to the body fluid and device sides of thehermetic feedthrough 132. The device side portion of the terminal pin142 further extends through a capacitor conductive pathway 150 of afeedthrough filter capacitor 140.

FIG. 9 is a quad polar feedthrough filter capacitor 140 mounted to ahermetic feedthrough 132 similar to that described in FIG. 7 exceptthat, in this case, the filter capacitor structure is round ordiscoidal. It is understood that a filtered feedthrough may comprise anyfilter capacitor shape instead of a round or discoidal filter capacitor,such as oval, rectangular, square and custom designed filter capacitorshapes.

FIG. 10 is a cross-sectional view taken generally from section 10-10 ofFIG. 9. There are four feedthrough terminal pins 142 each residing in afeedthrough conductive pathway 129, which extend through the feedthroughfilter capacitor 140. The feedthrough filter capacitor comprises groundelectrode plates 146 and active electrode plates 144.

As shown in FIG. 10, there are only three active electrode plates 144and four ground electrode plates 146. This low electrode plate countresults in a feedthrough filter capacitor 140 that has a relatively highESR at high frequencies. In an experiment conducted by the inventors, atypical EIA X7R 400-picofarad capacitor with only four electrode plateshad an ESR at 64 MHz of 4.8 Ohms. Re-design of the same geometry (size)capacitor with an EIA NP0 dielectric for a 400-picofarad capacitor withover 20 electrode plates resulted in an ESR at 64 MHz of approximately300 milliohms (0.3 Ohms). This sixteen to one reduction at 64 MHz is adramatic illustration of the importance of designing the AIMD MRIdiverter feedthrough filter capacitor 140 for low ESR. For example, foran X7R capacitor, the impedance is the square root of the sum of thecapacitor's reactance squared plus the ESR squared. A 400-pF capacitorhas a reactance of 2.49 ohms at 64 MHz. This results in a capacitorimpedance Z which is equal to −j2.49+4.8 or approximately 5.41 Ohms.Assuming an MRI induced RF voltage at the AIMD input at 64 MHz of 10Volts, the RF current diverted through the X7R capacitor is 10 Voltsdivided by 5.41 Ohms which is 1.85 Amps. The power dissipation due tothe X7R capacitor's ESR (I²R) is (1.85)²(4.8)=16.43 Watts. This amountof power dissipation is excessive for such a small component and willcause a temperature rise of over 20° C. On the other hand, a 400-pF NP0capacitor's impedance is equal to −j2.49+0.3 or Z=2.51 Ohms. This lowerimpedance will result in a much better filter (higher attenuation) andwill drop the RF voltage from 10 Volts to approximately 3.71 Volts. Thisvoltage drop is caused by the lead's characteristic impedance and thefact that more current has been drawn through this impedance. Thiscauses a voltage drop in the lead's characteristic impedance as measuredat the input to the AIMD. The RF current through the NP0 capacitor isthen 3.71 Volts divided by Z of 2.51 Ohms which is 1.48 Amps. The powerdissipation (I²R) is (1.48 Amps)²(0.3 Ohm) which equals 0.66 Watts whichwill result in a much smaller temperature rise. Accordingly, the low ESRdiverter feedthrough filter capacitor design (FIG. 32 labelled 210 andFIG. 34 labelled 210′) of the present invention offers the followingadvantages: (1) a much lower impedance at 64 MHz and therefore a moreeffective EMI filter; (2) higher attenuation, therefore acts to reducethe MRI induced RF voltage at the input to the AIMD; and (3) as will beshown, the diverter feedthrough filter capacitor 210, 210′ can bedesigned to conduct or convect heat away for dissipation over a largersurface area.

The above examples of ESR and impedance are just illustrative examplesof many thousands of possibilities. For active implantable medicaldevices, in general, capacitance values range anywhere from 300-pF to15,000-pF. Each design has a different physical geometry, size andnumber of internal electrode plates. In other words, there are manyother examples that have different values of ESR. The general principlesillustrated above, however, do apply across the board for all suchcapacitor design variations. Low k dielectrics will always mean a highernumber of electrode plates and therefore a lower ESR. That means thatthe low ESR designs will have much less heating of the capacitor itselfin an MRI environment.

The feedthrough filter capacitor 140 is bonded with an insulating washer162 (which comprises an insulative material) to the hermetic feedthrough132. An electrically conductive material 152, such as an electricallyconductive polyimide, an electrically conductive adhesive, anelectrically conductive epoxy, an electrically conductivethermal-setting polymer or a solder, attaches the outside diameterground capacitor metallization 166 of the feedthrough filter capacitor140 and the gold braze 154 a. The necessity to make an oxide-resistant(that is, an essentially oxide-free) attachment between the feedthroughfilter capacitor 140 and the ferrule 134 is described in U.S. Pat. No.6,765,779, the content of which is fully incorporated herein by thisreference. The insulator 156 of FIG. 10, such as an alumina ceramic, ishermetically sealed to the ferrule 134 by means of a gold braze 154 a.It is understood that the insulator 156 may alternatively comprise aglass or a glass-ceramic, which may form either a hermetic compressionseal or a hermetic matched seal. As glass-based seals are generallyfusion seals, instead of a hermetic gold braze 154 a, an oxide-resistantpocket-pad or a gold pocket-pad area 158 such as disclosed by FIG. 8 isused to make an oxide-resistant attachment to the feedthrough filtercapacitor 140. The four terminal pins 142 of FIG. 10 are hermeticallysealed to the insulator 156 via gold braze 154 b (as there are fourterminal pins 142, there are four gold brazes 154 b), each brazedterminal pin forming a feedthrough conductive pathway 129. The fourterminal pins 142 are attached to the active electrode plates 144 of thefeedthrough filter capacitor 140 using an electrically conductivematerial 168, such as an electrically conductive polyimide, anelectrically conductive adhesive, an electrically conductive epoxy, anelectrically conductive thermal-setting polymer or a solder. Theelectrically conductive material 168 electrically connects the activecapacitor metallization 164, which is electrically connected to theactive electrode plates 144 of the feedthrough filter capacitor, therebyforming four capacitor conductive pathways 150, each conductive pathwaycomprising one of the four terminal pins 142 of the hermetic feedthrough132.

Referring once again to FIG. 8, one can see that there are only twoactive electrode plates 144 and two ground electrode plates 146. A lowelectrode plate count is typically the case for prior art feedthroughfilter (diverter) capacitors 140 used in AIMD applications such ascardiac pacemakers, ICDs and the like, so that a capacitance value isgenerally kept low, as a high capacitance value loads down the output ofan AIMD. For example, too high of a capacitance value distorts pacemakertherapeutic pulses and also rob energy from the active implantablemedical system. An even more extreme example is in the case of animplantable cardioverter defibrillator, where a filter capacitance valueis too high such that the high voltage monophasic or biphasic shock waveform is seriously degraded. In the experience of the inventors, thecapacitance value for an AIMD diverter feedthrough filter capacitor 140is in a relatively narrow range from 10 picofarads to 20,000-picofarads.In most cases, the capacitance value is between 350 picofarads and10,000-picofarads. Having a capacitance value between these rangeseffectively attenuates most emitters from which AIMDs can be affected.This includes microwave ovens, cellular telephones and the like, whichtypically operate in the GHz frequency range. The thickness 170 of thefeedthrough filter capacitor 140, however, cannot be below a certainminimum or the barium titanate based ceramic capacitor dielectric body148 becomes too fragile. The entire hermetic feedthrough 132 and thefeedthrough filter capacitor 140 must be able to withstand thermalcycles and shocks including installation of the filtered feedthroughinto the AIMD housing 124 by a laser weld 157. Accordingly, it is veryunusual to see the thickness 170 of a diverter feedthrough filtercapacitor 140 less than 20/1000 of an inch (0.020 inches or 20 mils).Notwithstanding, when one looks at a cross-section of a typical priorart feedthrough filter capacitor 140 for human implant, one sees thatthere are very few electrode plates 144, 146 relative to the overallthickness 170 of said feedthrough filter capacitor. In fact, there areusually a number of blank dielectric cover sheets/layers 172 (blankmeaning that there are no electrode plates on the dielectric coversheets/layers) added on the top and/or bottom of the feedthrough filtercapacitor 140 consisting of ceramic material which is co-fired to addmechanical strength. There is a serious downside, however, to havingvery few electrode plates 144, 145, and that is that the high frequencyequivalent series resistance (ESR) of the capacitor increases. Forexample, prior art AIMD diverter feedthrough filter capacitors 140having significant dielectric and/or ohmic resistance at highfrequencies simply does not matter. This is because the power inducedfrom a typical emitter, such as a cellular telephone or microwave ovenresults in a trivial amount of RF current flowing through the diverterfeedthrough filter capacitor 140. Even in the most extreme examples,only a few milliwatts of heat is generated within the capacitorstructure itself. For high power RF current handling applications,however, for example, MRI conditional AIMDs that require diverting ofthe MRI induced RF energy, the capacitor dielectric loss and highfrequency ESR become critical and must be kept as low as possible.Accordingly, it is a feature of the present invention to have arelatively high number of electrode plates 144, 146 (generally greaterthan 10 active and 10 ground). It is noted, however, that a high numberof electrode plates in a feedthrough filter capacitor comprising a highk barium titanate based ceramic dielectric with a dielectric constant ofaround 2,500 as typically used in the prior art, results in a very high(too high) capacitance value. The present application resolves thisissue through the use of a relatively low dielectric constant material,such as EIA Standard NP0 material. NP0 material has a much lower k(generally, in the area of 60 to 90). A low k dielectric material isdefined herein as having a k greater than 0 but less than 1,000,referred herein as k<1,000. In some embodiments, a low k dielectricmaterial has a k greater than 0 but less than 200, k<200. In someembodiments, a low k dielectric material has a k greater than 0 but lessthan 100, k<100. Accordingly, in order to achieve a desired capacitancevalue (in the range of 350 picofarads to 10,000 picofarads or the rangeof 10 picofarads to 20,000 picofarads as previously disclosed), a muchgreater number of electrode plates is required. The higher number ofelectrode plates creates more parallel paths for RF current flow andgreatly reduces the ESR of the feedthrough capacitor. One is referred tothe equation illustrated in FIG. 22 to understand the relationshipbetween capacitance and the number of electrode plates and otherfactors.

FIG. 11 is a schematic diagram of the quad polar feedthrough capacitor140 of FIGS. 7-10. Feedthrough capacitors are three-terminal deviceslabelled in FIG. 11 as 141 a (terminal 1), 141 b (terminal 3), and 141 c(terminal 2).

FIG. 12 is a cross-sectional view of an embodiment of a novel hermeticfeedthrough installed in a housing of an AIMD taken from FIG. 17 of U.S.Pat. No. 8,653,384, the content of which is fully incorporated herein bythis reference. The outer surface of the insulator 156 (which may be aceramic insulator, for example, an alumina insulator) of the hermeticfeedthrough 132 has an insulator external metallization 167 disposed atleast partially on the outer surface of the insulator. The insulatorexternal metallization 167 may comprise two metallization layers, anadhesion metallization layer and a wetting metallization layer, whereinthe adhesion metallization layer may be disposed at least partially onthe outside surface of the insulator 156, and wherein the wettingmetallization layer may be disposed on the adhesion metallization layerso that during brazing a braze 154 (such as a gold braze) melts andhermetically bonds to the insulator 156 and the ferrule 134 of thehermetic feedthrough 132. The braze 154 contacting the insulatorexternal metallization 167 of the insulator 156 and the electricallyconductive ferrule 134 thereby forms the hermetic seal between theinsulator and the ferrule. It is understood that, while twometallization layers are illustrated, the insulator externalmetallization 167 may only comprise one metallization layer or maycomprise more than two metallization layers. The ferrule 134 may beinstalled into the AIMD housing 124 by forming a laser weld 157,however, other joining processes such as brazing, micro welding, microTIG welding, ultrasonic welding, resistance welding, friction welding,butt welding, arc welding, gas welding, projection welding, flashwelding, upset welding, solid state welding, diffusion welding,induction welding, percussion welding, electron beam welding,multi-stage brazing, or reactive brazing may be used. In thisembodiment, instead of a feedthrough leadwire 136 or terminal pin 142,this embodiment comprises a sintered paste-filled via 142′. It is anovel feature of this embodiment that this sintered paste-filled via142′ be of essentially pure platinum that is co-fired with theessentially high purity alumina ceramic substrate 156. As will be shownlater, a ceramic reinforced metal composite (CRMC) may alternatively beused instead of a high purity platinum to form the sintered paste-filledvia. Such sintered paste-filled vias offer customizable feedthroughconductive pathways design options while providing ease of manufacturingand cost-effective feedthrough design alternatives.

In general, hermetically sealed AIMDs have a body fluid side and adevice side. As used herein, the device side (inboard side) is locatedinside the conductive housing 124 of the AIMD, and the body fluid sideis located outside the conductive housing 124 of the AIMD. After laserwelding a hermetic feedthrough 132 to the conductive housing 124 of theAIMD, the feedthrough conductive pathways 129 (not labelled in FIG. 12),which comprise an electrical conductor, pass through the conductivepathway 129 to a body fluid side and to a device side. As previouslydisclosed, an electrical conductor of a hermetic feedthrough 132 may beselected from the group consisting of a leadwire, a lead wire, aterminal pin, a pin, a two-part pin, a lead conductor, a sinteredconductive via, a sintered paste-filled via, a co-sintered via, aco-sintered paste-filled via, a co-sintered via with one or moremetallic inserts, or combinations thereof. Thus, the feedthroughconductive pathway 129 through the insulator 156 of the hermeticfeedthrough 132 between the body fluid side and the device side can bemade from a leadwire 136, a terminal pin 142 or, as shown in FIG. 12, aconductive sintered paste-filled via 142′. The conductive pathway 129between the body fluid side and the device side can also be acombination of conductive inserts co-sintered within conductive pastesof the sintered past-filled via 142′. Accordingly, the distal end of thefeedthrough conductive pathways 129 on the body fluid side are externalof the AIMD housing 124 (hence is exposed to body fluid) and theopposite distal end of the feedthrough conductive pathways 129 on theinboard side or device side is located inside of the AIMD housing (henceis connectable to the AIMD electronic circuits residing internal to theAIMD housing).

FIG. 13 is a cross-sectional view of another embodiment taken from FIG.22 of U.S. Pat. No. 8,653,384, showing a hermetic feedthrough 132 and anattached filter 140 having a coated (metallized) bore filled withelectrically conductive material and a coated (metallized) bore withoutany fill in the bore. One is directed to U.S. Pat. No. 8,179,658, thecontent of which is fully incorporated herein by this reference, whichillustrates a capacitor bore and a solid feedthrough leadwire in thecapacitor bore. In this embodiment, the capacitor bore has nometallization, and the solid feedthrough leadwire is directly connectedto the capacitor active electrode plates by only the electricallyconductive material filling the un-metallized capacitor bore. Referringto the embodiment of FIG. 13, the feedthrough filter capacitor 140 ismounted directly to one or more of the co-sintered platinum filled viasof the insulator of the hermetic feedthrough as shown in the exemplaryco-sintered filled vias 142 a′, 142 b′ of FIG. 13. In this embodiment,an adhesively backed insulator washer 153 is used to affix thefeedthrough filter capacitor 140 onto the surface of the aluminasubstrate 156.

There are two different methods of electrical attachment to thefeedthrough filter capacitor illustrated in FIG. 13. In the left-handcapacitor bore, there is a solid fill of, for example, a solder, a brazeor a thermal-setting conductive material 155. Such a solid fillcapacitor bore may also be used for connection in the embodiments of the'658 patent, which have no capacitor bore metallization. A simplifiedelectrical attachment is shown on the right-hand capacitor bore, whereina solder bump or ball grid array (BGA) 151 is first dispensed at themetallized but un-filled capacitor bore and then the filter capacitor isaligned and placed over co-sintered paste-filled vias of the hermeticfeedthrough as shown. Then, a temperature is applied to reflow thesolder into place. The solder makes electrical contact with theco-sintered paste-filled filled via 142 a′, 142 b′ and also with theactive capacitor metallizations (terminations) 164 of the metallizedun-filled capacitor bore.

In accordance with good EMC principles, the feedthrough filter capacitor140 is disposed immediately at the point of EMI ingress into the insideof the device housing 124. In this way, high frequency EMI can bedecoupled and diverted to the device housing 124 without adverselyaffecting AIMD sensitive electronic circuits. Feedthrough filtercapacitor active electrode plates 144 a and 144 b are both eachconnected to the active capacitor metallization 164 of their respectivecapacitor bores. The capacitor ground electrode plates 146 make contactwith the ground capacitor metallization 166. An electrically conductivematerial 152 provides electrical connection to the ground capacitormetallization 166 and to the gold braze 154 of the ferrule 134, whichmakes a low impedance and low resistance essentially oxide-freeelectrical connection, required for superior high frequency performance.

FIG. 14 is a prior art multi-layer ceramic capacitor (MLCC) 140′. MLCCchip capacitors are made by the hundreds of millions per day to serviceconsumer electronics and other markets. Virtually all computers, cellphones and other types of electronic devices have many MLCC chipcapacitors. One can see that the MLCC chip capacitor 140′ has a bodygenerally consisting of a high dielectric constant ceramic body 148′such as barium titanate. The MLCC chip capacitor 140′ also has a pair ofsolderable terminations (the active capacitor metallization 164 and theground capacitor metallization 166) at either end. These solderableactive and ground terminations, that is the active capacitormetallization 164 and the ground capacitor metallization 166, provide aconvenient way to make an electrical connection to the internalelectrode plates 144, 146 of the MLCC chip capacitor 140′. The filtercapacitors of FIG. 14 can also comprise other shapes and types of filtercapacitor technologies, including rectangular, cylindrical, round,tantalum, aluminum electrolytic, stacked film or any other suchcapacitor shapes and technologies. It is understood by those skilled inthe art that the MLCC chip capacitor 140′ can be flipped such that thecorresponding capacitor metallizations 164 and 166 are reversed, as itis only when the MLCC chip capacitor 140′ is installed that one canidentify which metallization is the active capacitor metallization 164and which metallization is the ground capacitor metallization 166.

FIG. 15 is a cross-sectional view taken from section 15-15 of FIG. 14.The MLCC 140′ includes left-hand side electrode plates 144 andright-hand side electrode plates 146. One can see that the left-handside electrode plates 146 are electrically connected to an externalcapacitor metallization 164. The right-hand side electrode plates 146are shown connected to the external capacitor metallization 166. Priorart MLCC 140′ and equivalent chip capacitors are also known astwo-terminal capacitors. That is, there are only two ways electricalenergy can connect to the body of the capacitor. In FIGS. 14 and 15, thefirst terminal 174 is on the left-hand side and the second terminal 176is on the right-hand side of the capacitor. As defined herein, MLCC chipcapacitors are two-terminal devices. In contrast, feedthrough filtercapacitors are three-terminal devices, which have very lowself-inductance and make excellent high frequency EMI filters.

FIG. 16 is the schematic diagram of the MLCC 140′ illustrated in FIGS.14 and 15.

FIG. 17 illustrates another type of prior art three-terminal filtercapacitor known as a flat-through capacitor 140″. The flat-throughcapacitor 140″ is connected to circuit traces 178 a, 178 b at activecapacitor metallizations 164 a, 164 b at each end of the flat-throughcapacitor forming an active circuit path. A circuit current 180 passesall the way through the capacitor 140″ along the active circuit path asillustrated. The capacitor 140″ is also connected to ground circuittraces 182 a, 182 b at ground capacitor metallizations 166 forming aground circuit path. The overlap of the active electrode plates and theground electrode plates creates the capacitance of the flat-throughcapacitor 140″.

FIG. 18 illustrates the internal electrode plates of the flat-throughcapacitor 140″ of FIG. 17. Ground electrode plates 146 are connected toground capacitor metallizations 166. The through active electrode plates144 are connected to active capacitor metallizations 164 a, 164 b. Theelectrode plate embodiment of the flat-through capacitor 140″ of FIG. 17comprises a through or active electrode plate 144 sandwiched between twoground electrode plates 146. As previously disclosed, the through oractive electrode plate 144 is connected at both ends of the flat-throughcapacitor by the active capacitor metallizations 162 a, 162 b, which areterminals 1 and 2 respectively of the flat-through capacitor 140″. Whenthe flat-through capacitor is mounted between the circuit traces 178 a,178 b as shown in FIG. 17, the active circuit path is made. Referring tothe active electrode plate of FIG. 18, one can see the current i₁ entersat 164 a (terminal 1). If the current is a high frequency EMI current,it is attenuated along the length of the flat-through capacitor by thecapacitance of the flat-through capacitor and emerges as a much smalleramplitude EMI signal at 164 b (terminal 2) as current i_(1′).

FIG. 18A is the schematic of the three-terminal flat-through capacitorof FIG. 17. One can see that the flat-through capacitor is a truethree-terminal device consisting of terminals 164 a (terminal 1), 164 b(terminal 2) and ground 166 (terminal 3). The circuit current 180 passesthrough the active electrode plate 144 from the first terminal 164 a tothe second terminal 164 b. The ground terminal which is the thirdterminal, is the AIMD housing 124. As shown, the circuit currenti₁-i_(1′) passes all the way through the flat-through capacitor, asillustrated.

FIG. 19 illustrates a method of attaching MLCCs 140′ directly to thehermetic feedthrough 132. In accordance with the present invention, theMLCCs 140′ are relatively low dielectric constant (low k), like NP0,such that they have a high number of electrode plates thereby minimizingcapacitor ESR. This makes MLCC chip capacitors very effective indiverting high levels of RF current at an MRI RF-pulse frequency. One isreferred to U.S. Pat. Nos. 5,896,267 and 5,650,759, both to Hittman etal., which more thoroughly describe the use of MLCC chip capacitors asfeedthrough filter capacitors attached at or near the hermeticfeedthrough of an active implantable medical device. The contents ofthese two patents are fully incorporated herein by these references.

FIG. 19A is the schematic diagram of the bipolar MLCC chip capacitors140′ of FIG. 19. As shown, these are two-terminal capacitors withterminal 1 connected to the terminal pin 142 and terminal 2 connected toground, which is also the AIMD housing 124.

FIG. 20 is a cross-section of a typical MLCC chip capacitor 140′, suchas those of FIGS. 14 and 19. It is noted, as previously disclosed, thatthe ESR of the capacitors of FIGS. 14 and 19 is high due to a low numberof electrode plates 144, 146. The design principles illustrated in thiscross-section are equally applicable to any type of feedthrough filtercapacitor 140, including the filter capacitors described in FIGS. 7 and9 of the present application. In general, the equivalent seriesresistance (ESR) of a filter capacitor depends upon a number of veryimportant variables. A filter capacitor's ESR is the sum of theconnection resistance (R_(c)) 184, the resistance of attachment material(R_(a)) 186, the resistance of capacitor metallization (used to attachto internal electrode plates) (R_(m)) 188, the electrode resistance(R_(e)) 190 and 190′ of the electrode plates 144 and 146 and also theresistance of the dielectric loss tangent (R_(DL)) 192. There is alsoanother type of resistance (not shown) which occurs at very highfrequency, known as skin effect (R_(s)). Skin effect is understood bythose skilled in the art as the tendency of a high-frequency current toflow near the surface of a conductor as opposed to the interior of aconductor resulting in an increase of resistance in the conductor withincreasing frequency. Hence skin effect is a situation in which the bulkof the current flow is on the skin (near the surface) of the electrodeplates and the circuit connections instead of uniformly distributedthroughout the full body of the conductor. This also has the effect ofincreasing a capacitor's ESR. In general, for typical MRI RF-pulsefrequencies, skin effect can be ignored (as skin effect is mostly agreater than 500 MHz phenomenon).

FIG. 21 is the schematic diagram of the MLCC chip capacitor 140′ of FIG.20 showing that the capacitor's ESR is the sum of the connectionresistance (R_(c)) 184, the connection material resistance (R_(a)) 186,the capacitor metallization resistance (R_(m)) 188, the electroderesistance (R_(e)) 190 and the capacitor's dielectric loss resistance(R_(DL)) 192. The capacitor's dielectric loss resistance (R_(DL)) 192 isfrequency variable, which will be explained in further detail. For awell-designed and properly installed filter capacitor, many of theseresistances are so small that they can be ignored. For example,referring once again to the MLCC chip capacitor 140′ of FIG. 20, if thecapacitor metallizations 164, 166 are well designed and are properlyattached to the filter capacitor, then the capacitor metallizations willhave a trivially small resistance (R_(m)) 188. In a similar fashion, ifthe electrical attachment material 152 is a solder or a properthermal-setting conductive adhesive, the attachment material resistance(R_(a)) 186 will also be a trivial amount. If the system is attached togold or another similar oxide-resistant material, then the connectionresistance (R_(c)) 184 will also be trivially small. Referring onceagain to MLCC chip capacitor 140′ of FIG. 21, the total ohmic loss R_(o)200, therefore, consists almost entirely of the total electrode plateresistance (R_(e))_(total) 190 190′. This is why it is so important inthe present invention to maximize the number of electrode plates of alow k filter capacitor. A low k filter capacitor is defined herein ascomprising a low k dielectric material having a k<1,000. In someembodiments, a low k capacitor comprises a dielectric material having ak<200. At high frequency, the ohmic loss of the low k filter capacitoris almost entirely due to the resistive loss of the active and groundelectrode plates (R_(e))_(total) 190, 190′.

FIG. 22 provides the equation relating capacitance C to the dielectricconstant k, the active area A, which is the overlap area of the activeelectrode plate and the ground electrode plate of a capacitor, thenumber of electrode plates n and the dielectric thickness d of thefilter capacitor. Since the dielectric constant k is directly related tothe capacitance C, one can see how dramatically the capacitance of acapacitor rises when the dielectric constant k is 2,500 as opposed, forexample, to a dielectric constant k below 200 such as an EIA Class Idielectric. Assuming a constant capacitor dielectric thickness d for aparticular filter capacitor voltage rating, the only way to increase thecapacitance of a filter capacitor comprising a dielectric having a kbelow 200 so that the original capacitance value of the filter capacitorcomprising the dielectric having a k of 2,500 is achieved requiresgreatly increasing the number of electrode plates in this capacitorcomprising the dielectric having k less than 200. In the prior art,using a dielectric having a k less than 200 in a feedthrough filtercapacitor is counterintuitive. However, in the present invention, acapacitor having a dielectric with a k less than 200 is exactly what wewant to do. A high number of electrode plates drives down the highfrequency ohmic losses of the filter capacitor and thereby greatlyincreases the efficiency of the filter capacitor comprising such low kdielectrics so that RF energy can effectively be pulled out of animplanted lead during MRI scans. In addition, the high number ofelectrode plates of such a filter capacitor has a very low equivalentseries resistance at the MRI RF-pulse frequency, thereby significantlyreducing the amount of heat produced in, for example, a low k diverterfeedthrough filter capacitor 140 or a low k diverter MLCC chip capacitor140′.

FIG. 23 illustrates the schematics of an ideal capacitor 194 and also areal (non-ideal) capacitor 196 which consists of an ideal capacitor 194in series with its ESR 198. For the purpose of the present discussion, acapacitor's series inductance or insulation resistance (a parallelresistance) can both be ignored. This is because the inductance offeedthrough filter capacitors is quite low at MRI RF-pulse frequencies.Further, the filter capacitor's insulation resistance is generally inthe megohms or gigohms range, which is so high, it can also be ignoredas a parallel path. Also shown in FIG. 23 is a graph of the impedanceplane showing the capacitor ESR in the real axis and the capacitivereactance −jX_(C) shown on the imaginary axis. The capacitor's losstangent δ is also illustrated.

In FIG. 24, equations are given for capacitive reactance X_(C),impedance Z, dissipation factor DF and loss tangent of δ, which is alsodefined as the dissipation factor DF. Historically, dissipation factorhas been expressed as a percent, such as 2.5% maximum. This means thatthe allowable dissipation factor is 2.5% of a capacitor's capacitancereactance at a particular frequency. Usually, due to dielectric losses,this number is dominated at low frequencies by the capacitor'sdielectric loss. The capacitor's dielectric loss is generally related toits dielectric constant and the frequency of the driving energy. Forexample, if the frequency of an applied sinusoid is relatively low (say60 Hz), then the crystal lattice of the capacitor has plenty of time todeflect back and forth under the electrical stress and, in so doing,produces a significant amount of heat, which is a type of real orresistive loss. At 1 kHz, the capacitor dielectric structure (ordipoles, if one uses that theory) vibrates at a higher frequency. As onegoes higher and higher in frequency, say to 10 MHz, then for the low kClass I dielectrics of the present invention, there is very littlemovement in the crystal lattice and, accordingly, very little heatgenerated due to dielectric loss. It will be further illustrated howdielectric loss varies with frequency. In the past, particularly asdescribed by testing specifications such as MIL-STD-202 and MIL-STD-220among others, dissipation factor is measured either at 1 kHz, or in somecases, at 1 MHz. Unfortunately, this data is misleading at MRI RF-pulsefrequencies, which generally are 21.28 MHz (0.5 T), 64 MHz (1.5 T), 128MHz (3 T) or higher. For most dielectrics, the high frequency ohmicloss, due to the capacitor's electrode plates, is so low that it ismasked by the capacitor's dielectric loss when measured at lowfrequencies such as 1 kHz or 1 MHz. This will be explained in subsequentfigures.

FIG. 25 is a more complete schematic for an MLCC chip capacitor 140′,which has been simplified from FIG. 21. (R_(o)) represents total ohmicloss 200 which is the sum of the ohmic losses by connection resistance(Re) 184, the attachment material resistance (R_(a)) 186, themetallization resistance (R_(m)) 188, and the electrode resistance(R_(e)) 190. Assuming that the connection resistance (R_(c)) 184 is verylow, such as in an attachment to gold, and that the attachment materialresistance (R_(a)) 186 has a very low resistivity, such as athermal-setting conductive adhesive or a solder, and assuming that thecapacitor metallization materials have very little ohmic resistance tothe electrode plates, then one can assume that the bulk of the totalohmic loss (R_(o)) 200 of the MLCC chip capacitor 140′ is equal to theentire electrode stack of said MLCC chip capacitor, meaning that thetotal ohmic loss (Ro) 200 is essentially equal to the electroderesistance (R_(e))_(total) 190 of the MLCC chip capacitor 140′. Aspreviously disclosed, the resistance of the electrode stack of thecapacitor depends on the length, the width and the thickness of theelectrode plates and also, importantly, on the number of electrodeplates that are in parallel. Therefore, reducing the dielectric loss andmaximizing the number of electrode plates are key features of the filtercapacitor embodiments of the present invention.

FIG. 26 is a simplified schematic diagram of FIG. 25 showing that theESR 198 of the MLCC chip capacitor 140′ is the sum of the dielectricloss tangent resistance (RDL) 192 plus the total electrode resistance(R_(e))_(total) 190 of the parallel electrode stack of said MLCC chipcapacitor. Referring once again to FIG. 25, one can see that there is aresistor in parallel with the ideal capacitor C 194. This resistorcomprises an insulation resistance (R_(IR)) 202, which is the insulationresistance of the MLCC chip capacitor 140′. In a high-quality capacitor,this insulation resistance value tends to be in the hundreds of megohmsor higher and does not significantly contribute to the capacitor ESR,therefore, for the purpose herein, can be ignored as part of the filtercapacitor equivalent circuit model. The (R_(IR)) also has negligibleeffect on capacitor high frequency performance. For three-terminal orphysically small MLCC chip capacitors, the equivalent series inductance(ESL) 204 shown in FIG. 25 can also be ignored because inductivereactance is very low at low frequencies and filter capacitor inductancecan be considered negligible at high frequencies. Accordingly, the ESR198 of the AIMD diverter MLCC chip capacitor 140′ of FIG. 26 is the sumof the dielectric loss tangent resistance (R_(DL)) 192, the total ohmicloss (R_(o)) 200 and any losses due to skin effect (R_(s)), which is notlabelled in FIG. 26. Specifically, regarding skin effect, at lowfrequencies, skin effect is negligible, and for physically small MLCCchip capacitors and feedthrough filter capacitors, skin effect does notreally play a role until one gets to very high frequencies, for example,above 200 MHz. It is noted, therefore, that for the MRI RF frequencies21.28 MHz (0.5 T), 64 MHz (1.5 T), and 128 MHz (3 T), skin effect (Rs)is negligible and may be ignored, which is why FIG. 26 does not label(R_(s)). Hence, assuming that the filter capacitor has goodmetallization, essentially oxide-free connection to the ferrule and goodelectrical attachment materials, then the total ohmic loss (R_(o)) 200is completely dominated by the electrode resistance (R_(e)) 190. Thus,for the purpose of the present invention, at MRI RF frequencies the ESR198 of the filter capacitor is generally equal to the dielectric losstangent resistance (R_(DL)) 192 plus the electrode resistance (R_(e))190. Both of these parameters, (R_(DL)) and (R_(e)), must be carefullycontrolled for the high-power RF diverter MLCC chip capacitor 140′ ofthe present invention.

In summary, it has been shown that dielectric loss is a frequencyvariable and that, for at least the MRI RF-pulse frequencies 21.28 MHz(0.5 T), 64 MHz (1.5 T), and 128 MHz (3 T), the dielectric loss for alow k EIA Class I ceramic filter capacitor drops to a very low value(essentially zero) such that the ESR 198 of a diverter low k filtercapacitor is primarily determined by the total resistance of itselectrode plates.

FIG. 27 is a more detailed illustration of the dielectric loss in ohmsof a relatively low k ceramic filter capacitor. One can see, at lowfrequencies, the dielectric loss in ohms can be over 100 ohms or evenmuch greater. However, as one increases in frequency, one can see thatthe dielectric loss drops and is nearly zero at 64 MHz (the RF-pulsefrequency of a 1.5 T MRI scanner).

FIG. 28 shows a U-shaped composite curve. The composite curve is thesummation of filter capacitor ohmic loss, which includes the totalresistance of capacitor electrodes, capacitor metallization, electricalattachment materials, and electrical connection. As one can see, andignoring skin effect, the conductor ohmic loss for the filter capacitoris relatively constant from low frequency all the way to very highfrequencies. For an EIA Class I dielectric, the filter capacitordielectric loss (marked with small squares) is a very high value at lowfrequency, and then drops to near zero at MRI RF frequencies such as 64MHz and 128 MHz. Skin effect is also shown, which is an ohmic loss fortwo-terminal type filter capacitors. The total ESR is the solid line,which is the summation of the capacitor dielectric loss, the capacitorconductor ohmic loss and skin effect. The present invention is directedto make sure the center of this total ESR U-shaped curve includes therange of MRI RF-pulse frequencies at the near zero value.

FIG. 29 is a table showing an example of losses (which are measuredlosses) for a prior art 2,000-picofarad X7R (2,500 k) feedthrough filtercapacitor. One can see that at the 1 kHz frequency, the X7R capacitordissipation factor DF loss is about 1591.55 ohms and the ohmic loss is0.432 ohms. When the dissipation factor DF loss is added to the ohmicloss, the X7R capacitor equivalent series resistance (ESR) is about1591.98 ohms. Even at 1 MHz frequency, the X7R capacitor measures adissipation factor DF loss of about 1.59 ohms, which, when added to theohmic loss of 0.432 ohms, yields an ESR of about 2.024 ohms. It becomesapparent that at both the 1 kHz and 1 MHz frequencies the X7R capacitordissipation factor DF losses dominate the ohmic losses. As a result, theohmic loss is essentially hidden or indistinguishable due to such asignificantly higher DF loss at these frequencies. It is not until afrequency of at least 10 MHz that the DF loss no longer dominates thecapacitor ESR measurement and the ohmic loss of the X7R filter capacitorbecomes discernable. This is very important in understanding a filtercapacitor's real losses. As shown by FIG. 29, at a testing frequencygreater than 10 MHz, the X7R filter capacitor has an ESR ranging fromabout 0.59 to about 0.44 ohms, which is still significant. Referringonce again to the curve of FIG. 28, an ESR ranging from about 0.59 toabout 0.44 ohms at frequencies from 10 MHz to 500 MHz substantiallyraises the center of the U-shaped curve away from the near zero ESRvalue desirable for effectively diverting RF energy induced in AIMDleads at MRI RF-pulse frequencies. Hence, as one can see, despite thespecifications of MIL-STD-202 and MIL-STD-220 among others, measuring anAIMD filter capacitor's losses at 1 kHz and 1 MHz is not a useful way toanalyze a filter capacitor's actual losses at MRI RF-pulse frequencies.In summary, to properly assess filter capacitor losses at MRI RF-pulsefrequencies, one needs to analyze loss measurements in the range of 10MHz to 500 MHz because at frequencies above 10 MHz the dissipationfactor drops and the ohmic losses of the capacitor become visible makingit easier to distinguish between acceptable and unacceptable capacitorhigh frequency performance.

FIG. 30 dramatically illustrates the difference in capacitor performancewhen one uses an EIA Class I dielectric, such as C0G (NP0), which has adielectric constant of less than 200. Because of this low dielectricconstant, a high number of electrode plates of the capacitor isnecessary to achieve the filtering performance required for AIMDs. Thehigh number of electrode plates has the effect of greatly reducing thecapacitor's ohmic losses. In addition, EIA Class I dielectrics have alower dissipation factor, particularly at high frequency. Comparing 100MHz frequency measurements of the X7R capacitor of FIG. 29 and the C0G(NP0) capacitor of FIG. 30, one can see that the ESR of the C0G (NP0)capacitor is about 0.201 ohms vs. an ESR of about 0.45 of the X7Rcapacitor. The ESR of the C0G (NP0) capacitor is reduced by more than50% the ESR of the X7R capacitor, which, for AIMD applications, isconsidered a significant ESR reduction. By also increasing the number ofelectrode plates (see capacitors 210, 210′ in FIGS. 32, 34-36), the ESRof the C0G (NP0) capacitor may be further reduced to below 0.1 ohms.Thus, the dielectric material C0G (NP0) and the increased number ofelectrode plates of the AIMD diverter feedthrough filter capacitor ofthe present application substantially lowers capacitor ESR and willsignificantly reduce heat generation in said AIMD diverter feedthroughfilter capacitor (for example, the feedthrough filter capacitor 210,210′ or even 210″ and 210′″ of the present application).

Further regarding the present invention, the inventors have contemplatedusing a dielectric material having dielectric constant k<1,000 forfilter capacitors. The inventors have developed a mid k dielectricfilter capacitor for making filter capacitors for use in AIMDs (forexample, the feedthrough filter capacitor 210, 210′, 210″ and 210′″ ofthe present application). The mid k dielectric filter capacitor is onthe order of 500, comprising a dielectric constant of approximately 500to as much as 700. The inventors used various dopants and firingconditions, such that, the new mid k dielectric provides an ohmic loss(R_(o)) of less than 100 milliohms at frequencies from 10 MHz to 100MHz. In some embodiments, the inventors have achieved resistance losseson the order of 50 milliohms. Since the dielectric loss at the 10 MHz to100 MHz frequency range is nearly zero, this means that the total ESR ofthe new mid k capacitors essentially only reflect the ohmic loss (Ro),thus are the order of 50 milliohms to as much as 100 milliohms at MRIRF-pulse frequencies. As, for example, a 1.5 Tesla MR scanner has anRF-pulse frequency of 64 MHz, it is very important to have lowresistances in order to minimize capacitor heating as the AIMD divertercapacitor diverts the RF-pulse frequency during an MRI scan. This isaccomplished by the capacitors of the present application having adielectric material of a dielectric constant k<1,000.

FIG. 31 is an equivalent series resistance (ESR) versus frequency graphfrom a frequency sweep done on a low k feedthrough filter capacitor 210of the present application using an Agilent E4991A materials analyzer.At a start frequency of 1 MHz (curve 136), one can see that the ESR ofthe low k feedthrough filter capacitor 210 is on the order of 6 ohms,which is considered very high. However, by the time one reaches about21.28 MHz (the frequency of a 0.5 T MRI scanner), the ESR of the low kfeedthrough filter capacitor comprising an EIA Class I dielectric beginsto flatten out. As dielectric loss at about the 10 MHz to 100 MHzfrequency range is nearly zero, the only loss reflected by curve 136 isthe ohmic loss of the low k feedthrough filter capacitor 210, which at100 MHz is only 200 milliohms. It is noted that the ESR of saidcapacitor is also 200 milliohms at the RF-pulse frequencies for a 1.5Tesla scanner (64 MHz) and a 3 Tesla scanner (128 MHz).

Since the 1960s, as previously mentioned, it has been a common practicein the capacitor industry to measure capacitance and dissipation factorat 1 kHz. The dissipation factor is usually defined as a percentage, forexample, 2.5% maximum. What this means is that the dielectric lossresistance can be no more than 2.5% of the capacitive reactance at acertain frequency (which characteristically has been 1 kHz). As anexample, if the capacitive reactance for a particular capacitor is80,000 ohms at 1 kHz with a 2% dissipation factor this equates to 1,600ohms of resistance at the 1 kHz frequency. Referring once again to FIG.28, it is noted that the dielectric loss essentially goes to about zeroat high frequency. For typical low k dielectric constant EIA Class 1ceramic capacitors, frequencies above 10-20 MHz is sufficiently high sothat the dielectric loss is no longer a dominating factor in thecapacitor ESR measurement. Hence, as the ESR of a capacitor varies withthe capacitance value, the number of electrode plates, and the lengthand width of the electrode plates, a wide range of “normal” ESR readingscan be obtained for many types of capacitors by using the teachings ofthe present application (see the filter feedthrough capacitors 210,210′, 210″ and 2101. For example, one particular capacitor may have anormal ESR reading of 0.05 ohms while another capacitor design may havea normal ESR as much as 10 ohms.

Referring once again to FIG. 31, one can see curve 137, which representsthe inventors new mid k dielectric (k on the order of 500 to 700). Ascan be seen, the new mid k dielectric, in general, yields filtercapacitors that have a total equivalent series resistance of less than100 milliohms between 10 MHz and 100 MHz frequencies. There are evencertain design configurations with a sufficient number of electrodeplates where the capacitor's ESR is between 10 and 50 milliohms in the10 MHz to 100 MHz frequency range.

Regarding number of electrode plates, maximization of the number ofelectrode plates in order to reduce the electrode resistance (R_(e)) ofan MLCC chip capacitor becomes paramount (shown in the low k MLCC chipcapacitor 210 of FIG. 32 and feedthrough filter capacitor 210′ in FIG.34). In general, in order to increase the number of electrode plates,the effective capacitance area (ECA) can be minimized and the dielectricconstant k lowered so that one ends up with a relatively high number ofelectrode plates. One might ask, why doesn't one simply make theelectrode plates much thicker in order to decrease their resistance? Itis true that making the electrode plates very thick reduces theirresistance, however, there is an undesirable consequence. The capacitoris longer monolithic and is simply like a sandwich or somewhat like adeck of cards that is ready to come apart at the first thermal shock orpiezoelectric effect. It is a basic tenet of ceramic engineering thatelectrodes be thin enough, and contain enough ceramic powder such thatwhen sintered, the ceramic capacitor structure becomes truly monolithic.This leaves the designer with only a few effective ways to control thecapacitor's ESR. For a given geometry, which is usually dictated by theAIMD design, there are very few degrees of freedom in the length, widthand geometry of capacitor electrode plates. Accordingly, in the presentinvention, maximizing the number of electrode plates becomes a keydesign factor. This goes hand in hand with the dielectric constant k ofthe capacitor. In other words, reducing the dielectric constant of acapacitor dielectric means that the number of capacitor electrode platesmust increase to achieve the same capacitance value as a capacitor usinga dielectric material having a high dielectric constant. The increase inthe number of electrode plates naturally reduces the ESR of thecapacitor and increases the ability of the capacitor to handle highlevels of RF current. Another reason to keep the ESR of the diverterfilter capacitor 210, 210′ extremely low is so the filter capacitor doesnot overheat while diverting high levels of RF currents to the housing124 of the AIMD 100, the AIMD housing being an energy dissipatingsurface (EDS). In the present application, feedthrough filter capacitorsand MLCC chip capacitors can act as high-power RF energy diverters.Energy diverters using an energy dissipation surface (such as a ferrule134 or an AIMD housing 124) are more thoroughly described in U.S. Pat.Nos. 8,219,208 and 7,751,903, the contents of which are fullyincorporated herein by these references. In a diverter filter capacitor,the RF currents are literally conducted through the electrode plates212, 214 of the filter capacitor 210, 210′ and hence through theelectrode plate resistance (Re) 190. Electrode plate resistance (R_(e))190 is the sum total of the resistance of all of the electrode plates212, 214 acting in parallel. If the electrode plate resistance (Re) 190is high, then there is a tremendous amount of I²R power loss that occursand the filter capacitor 210, 210′ rapidly gets very hot and perhapsdestroys itself and/or the surrounding electrical connections ormaterials. Another reason to keep the ESR 198 of the filter capacitor210, 210′ relatively low is so that the ESR represents a very lowimpedance Z at the MRI RF-pulse frequency. This will increase ability ofthe filter capacitor 210, 210′ to draw energy from the implanted lead110 and divert the energy to the energy dissipating surface of the AIMDhousing 124. If the filter capacitor represented too high of animpedance, which reduces the current, but also means that more energy isundesirably left in the implanted lead 110. Lowering the impedance Z ofthe diverter filter capacitor 210, 210′ also means that it is a betterEMI filter by offering increased attenuation at the MRI RF-pulsefrequency.

Even so, it is most important to keep the overall resistance 190 of theelectrode plates extremely low (in other words, extremely low ESR) sothat overheating of the primary filter capacitor 210 itself isprevented. It has been demonstrated that overheating of the filtercapacitor causes the adjacent AIMD housing 124 to also overheat. This ishighly undesirable in a human incision pocket. Typically, the AIMD isplaced under the skin, under the fat or even under a muscle. There arevarious FDA and CEM42 Standards that limit the amount of heat introducedto various types of body tissue. In general, the amount of heating islimited to 4° C. (that can vary with body tissue). For example, for adeep brain stimulator, a subdural implanted AIMD must have a much lowertemperature rise due to the extreme thermal sensitivity of brain matter.This is in contrast to a pectoral pocket created for cardiac pacemakeror ICD, which represents less thermally sensitive tissues and fats. Inany event, it is a major feature of the embodiments herein to preventthe overheating of the primary filter capacitor in order to minimize oreliminate heating of the AIMD housing 124.

In general, the filter capacitor 210, 210′ of the present invention mayhave at least 10 electrode plates. The filter capacitor comprises adielectric material having a k up to 1,000. It is contemplated that thefilter capacitor 210, 210′ may comprise an intermediate dielectricconstant (mid k) of say 400, 500 or even 600. A mid k dielectricmaterial makes it possible to design a capacitor with less than 10electrode plates, for example, 5 electrode plates (depending upon theirlength and width) and still have a low enough ESR in accordance with thepresent invention (meaning, 5 active electrode plates with 5 groundelectrode plates). Alternatively, the number of electrode plates can beas high as 20, 40 or even 100 or more; nonetheless, the criticalparameter is that the equivalent series resistance (ESR) of the filtercapacitor never exceeds 2 ohms at the MRI RF-pulse frequency. In someembodiments, the ESR can be <0.5 ohm. In some embodiments, the ESR is0.1 ohm.

FIG. 32 illustrates a cross-section of a multi-layer ceramic capacitorMLCC chip capacitor 210 of the present invention, which is similar tothe prior art MLCC chip capacitor 140′ illustrated in FIGS. 14, 19 and20, except that the number of electrode plates in the MLCC chipcapacitor of FIG. 32 is substantially increased to minimize ESR. Aspreviously disclosed, the number of electrode plates is a key factor forreducing capacitor ESR. Both the active electrode plates 212 and theground electrode plates 214 are substantially increased in order toreduce the ESR 198 of the MLCC chip capacitor 210 to less than 2 ohms atthe MRI RF-pulse frequency. In an embodiment, the ESR 198 of the MLCCchip capacitor 210 is less than 1 ohm. In addition to the increasednumber of electrode plates, the MLCC chip capacitor 210 comprises a lowk dielectric material (k<1,000) so that the capacitance value is not toohigh. In an embodiment, the dielectric material is an EIA Class Icapacitor such as NP0.

Referring once again to FIG. 32, one can see that the active electrodeplates 212 (on the left-hand side) and the ground electrode plates 214(on the right-hand side) are stacked in an interleaved relation. Anelectrical attachment material 152 connects the active capacitormetallization 164 to the terminal pin 142 on the left-hand side and theground capacitor metallization 166 to the ferrule 134 of a hermeticfeedthrough 132 on the right-hand side. In general, the electricalconnection material 152 is highly electrically conductive, but notnecessarily highly thermally-conductive. In summary, the MLCC chipcapacitor 210 of FIG. 32 is based on an EIA Class I dielectric, whichmeans its dielectric constant is relatively low and its temperaturecoefficient, in accordance with standard ANSI/EIA-198-1, published Oct.29, 2002, Table 2, namely, a permissible capacitance change from 25° C.(ppm/° C.) for Class I ceramic dielectrics. Thus, the maximum allowablecapacitance change varies from +400 to −7112 parts per million perdegree centigrade. As previously mentioned, an embodiment comprises theC0G dielectric, which is also commonly referred to as NP0.

FIG. 33 is an equation showing the effect of the parallel plateresistances. FIG. 33 gives the equation for the total resistance of theelectrode plates (R_(et)) of the MLCC chip capacitor being the summationof all parallel electrode plates 212, 214 (“n” electrode plates) of theMLCC chip capacitor.

FIG. 34 is very similar to the cross-section of the quad polarfeedthrough filter capacitor previously described in FIGS. 9-10, exceptthat the number of electrode plates 212, 214 have been increased inaccordance with the present invention such that the FIG. 34 quad polardiverter feedthrough filter capacitor 210′ has a high frequency ESR 198less than 2 ohms. Referring once again to FIG. 34, one can see that theoutside diameter ground capacitor metallization 166 is attached to agold pocket-pad area 158 of ferrule 134 using a conductive material 152.All of these connections, when properly done, have negligibleresistance. Accordingly, the ESR 198 of the feedthrough filter capacitor210′ at high frequency comprises the electrode resistance (R_(e)) 190 ofthe ground electrode plates 214 and the electrode resistance (R_(e′))190′ of the active electrode plates 212 all acting in parallel. Aspreviously stated, for EIA Class I dielectrics, the dielectric losstangent resistance 192 of the feedthrough filter capacitor 210′ can beignored at MRI RF-pulse frequencies since said dielectric loss tangentresistance becomes negligible at RF-pulse frequencies. Also, for afeedthrough filter capacitor geometry, skin effect (R_(s)) is alsonegligible. Referring once again to FIGS. 7-8, one can see a rectangularquad polar capacitor that is similarly attached to a gold pocket-padarea 158.

FIG. 35 is taken from section 35-35 of FIG. 34 and illustrates adoubling (dual electrode plates) of the active electrode plates 212 andthe ground electrode plates 214 of the feedthrough filter capacitor210′. Doubling the electrode plates 212, 214 is very effective sinceboth electrode plates are still exposed to the internal electric fieldsof the feedthrough filter capacitor; therefore, both the active and theground electrode plates, each having doubled plates, will moreeffectively support electrode plate displacement current flow (RFcurrents). Dual electrode plate capacitor designs greatly increase thenumber of electrode plates of a capacitor, which, as shown by theequation of FIG. 33, significantly reduces the overall total electrodeplate resistance (R_(et)). Dual electrodes are disclosed in U.S. Pat.No. 5,978,204 to Stevenson et al., the content of which is fullyincorporated herein by this reference. In the '204 patent, the dualelectrodes were utilized to facilitate high pulse currents, for example,in an implantable defibrillator application. Dual electrodes as appliedto the present application are very useful in driving down electroderesistance (R_(e)), thereby driving down the high frequency ESR 198 ofthe feedthrough filter capacitor 210′ while also enhancing conduction ofRF energy and/or heat 218 out of the feedthrough filter capacitor 210′during exposure to high power MRI RF-pulse environments.

FIG. 36 is very similar to FIG. 35, except in this case only the groundelectrode plates 214 have been doubled. Increasing the number of groundplates 214 is particularly efficient in the removal of RF energy and/orheat. As shown, the ground plates 214 are utilized to conduct heat awayfrom the diverter feedthrough filter capacitor 210′, directing the heatthrough the ferrule 134 of the hermetic feedthrough 132 to the housing124 of the AIMD 100, the housing 124 having a relatively large surfacearea for heat dissipation. The relatively large surface area of thehousing 124 of the AIMD 100 means that a great deal of RF energy and/orheat 218 can be dissipated without concentrating such energy in a smalllocation, which can lead to a very high temperature rise and possiblycause damage to surrounding body tissue.

FIG. 37 illustrates a family of lowpass filters 260 that all incorporatediverter capacitors of the present invention. As can be seen, theselowpass filters 260 incorporate a variety of capacitor designs rangingfrom a simple MLCC chip capacitor “C” to a three-terminal “feedthroughcapacitor-FTC”. These diverter capacitors (generally labelled 210 forsimplicity) can be combined in various ways with inductors to form “L”,“reverse L”, “T”, “Pi” (π), “LL”, “reverse LL” or “n” element lowpassfilters. In other words, as illustrated in FIG. 37, any of thehigh-power RF handling diverter capacitors of the present applicationcan be combined with any of the lowpass filter circuits of an AIMD forthe purpose of protecting the AIMD electronics from EMI, while at thesame time pulling MRI induced RF energy or heat from an implanted lead.

FIG. 38 is similar to FIG. 83 of U.S. Pat. No. 9,014,808, the content ofwhich is fully incorporated herein by this reference. The electricalschematic of FIG. 38 represents the simplest form of the lowpass filtersof FIG. 37. Represented is a lead in connection with an AIMD hermeticfeedthrough 132, which is in connection with a lowpass filter 260, whichcan comprise any diverter capacitor of FIG. 37. FIG. 38 illustrates thegeneral lowpass filter 260 being an exemplary feedthrough filtercapacitor 210′ which is connected in series with a bandstop filter 258,which is, in turn, connected with an L-C trap filter 262 disposedbetween the circuit trace or leadwire and the AIMD housing 124.

FIG. 39 shows a dual chamber bipolar cardiac pacemaker 100C with leadsimplanted into the right atrium and right ventricle of the heart 112. Asshown, header block 138 comprises industry standard IS-1 connectors 126a, 128 a, 126 b, 128 b. MRI energy is shown being induced on theimplanted leads 110 and 110′. As this energy enters the pacemakerhousing 124, it encounters diverter capacitor 210′. The divertercapacitor 210′ is designed to dissipate high RF energy or heat inaccordance with the present invention. Accordingly, diverter capacitor210′ has a low dielectric loss at high frequency and also very low highfrequency ESR. In this case, there is a secondary row of MLCC chipcapacitors 210 a through 210 d that are mounted on the AIMD circuitboard 130 at a location distant from the primary diverter capacitor210′. In this case, the primary diverter capacitor 210′ can have a lowercapacitance value with the rest of the capacitance comprising eithercircuit board mounted capacitors 210 a through 210 d or other similarelectrical components. As illustrated, the AIMD circuit board 130comprises a ground circuit trace 182 that is connected through a lowimpedance RF conductor, which in FIG. 39 is an RF grounding strap 264,that conducts the RF energy or heat to the AIMD housing 124. This lowimpedance RF grounding strap 264 is important to conducting MRI RFcurrents efficiently to the housing 124 of the AIMD 100C. In order tospread out heat, multiple low impedance RF conductors can be used (notshown) of various shapes and configurations, and in any shape andconfiguration combination. A major advantage of the embodiment shown inFIG. 39 is that by spreading out the filtering function, RF energy/heator MRI RF energy induced heat is dissipated or spread out over muchlarger areas. This avoids hot spots on the AIMD housing 124. Referringonce again to FIG. 39, it is appreciated that if the capacitance valueof the primary filter capacitor 210′ (which can be a feedthroughcapacitor, an MLCC chip capacitor, an X2Y attenuator, a flat-throughcapacitor or combinations thereof) is sufficiently large, then the MLCCchip capacitors 210 shown on the circuit board 130 are not necessary.Alternatively, if the circuit board 130 was placed immediately adjacentto the ferrule 134, then it is possible to eliminate the feedthroughcapacitor 210′ and instead have an MLCC chip capacitor, an X2Yattenuator, a flat-through capacitor or combinations thereof eachassociated with one of the quad polar leads to act as high frequency RFenergy diverters. In summary, referring back to FIG. 39, it isappreciated that one can have a primary filter capacitor 210′ that isbacked up by one or more onboard chip capacitors 210 or only afeedthrough capacitor 210 or only one or more board-mounted chipcapacitors, for example, MLCC chip capacitors 210 a through 210 d.

FIG. 39A is the electrical schematic of one of the leadwire circuits 136a of the cardiac pacemaker 100C of FIG. 39. The first low ESRfeedthrough filter capacitor 210′ is shown in parallel with atwo-terminal capacitor 210 a. It is appreciated that all four of thequad polar leads 136 a through 136 d have the same electrical schematicparallel representation.

Referring once again to FIG. 39, it is noted that at least two of theleadwires 136 a through 136 d extend through the hermetic feedthrough132 in non-conductive relationship with the ferrule 134 and thenextending through respective bores of the feedthrough filter capacitor210′. These leadwires 136 a through 136 d then extend to the deviceside, which is inside the AIMD housing 124, and each are electricallyconnected to either a via hole or circuit trace land of the AIMD circuitboard 130. Each via hole or circuit trace land on circuit board 130 areelectrically connected to a capacitor metallization of one of the MLCCs210 a through 210 d by leadwires 142 a through 142 d. For the purposesof this invention, we will refer to the internal electrode plates of theMLCC chip capacitors 210 as having ground electrode plates and activeelectrode plates. The ground electrode plates are connected to the MLCCchip capacitor's end termination and are therefore electricallyconnected to the ground circuit trace 182. The capacitor's activeelectrode plates are electrically connected to at least two leadwires ofthe leadwires 142 a through 142 d. It is appreciated by those skilled inthe art that circuit board 130 can be an alumina ceramic board, a singlelayer board, a multi-layer board, fiberglass or FR4 or any number ofmaterials of which circuit boards are made. It will also be appreciatedthat a connection from the active side of the capacitors 210 can beaccomplished by a flex cable (not shown). In such an embodiment, theflex cable replaces the leadwires 142 a through 142 d on the device side(the inside or inboard side) of the AIMD housing and the flex cableconnects to shortened leadwires adjacent the feedthrough filtercapacitor 210′. The use of a flex cable greatly simplifies andfacilitates the assembly of the AIMD internal circuits. It should alsobe noted that the ground circuit traces 182 and the embedded circuittraces 178 of circuit board 130 (and other circuit traces not shown) canbe made from a variety of materials. Since these are inside thehermetically sealed and biocompatible AIMD housing 124, the circuittraces need not be biocompatible themselves. In fact, they can be madeof copper, silver, platinum or any other highly conductive material. Inan alternative embodiment (FIG. 39B), the chip capacitors 210 a through210 d of the circuit board 130 of FIG. 39 can instead be mounteddirectly to the flex cable 171 of FIG. 39B.

FIG. 39B illustrates a unipolar hermetic feedthrough consisting of aferrule 134, an alumina insulator 156 and a leadwire 136, wherein, theleadwire is labelled 136 on the body fluid side and the same leadwire islabelled 142 on the device side (or inboard side). Shown is a flex cable171, wherein a first circuit trace (an active circuit trace 143) isconnected to the hermetic device side terminal pin 142 of thefeedthrough. There is also a second circuit trace (a ground circuittrace 182) which is connected to the ferrule 134, which is the groundconnection (the potential of the ferrule 134 is the ground potential).Importantly, the ferrule 134 is welded to the AIMD housing 124. The MLCCchip capacitor 210, which has a k<1,000 in accordance with the presentinvention, is shown electrically connected between the ground circuittrace 182 and the active circuit trace 143 using an electricallyconductive material 152. Electrical connection material 152 can be asolder, a thermal-setting conductive adhesive, a thermal settingconductive epoxy, a thermal setting conductive polymer or similar suchconductive material.

Referring once again to FIG. 39, one can see that the MLCC chipcapacitors 210 a through 210 d are a considerable distance from thepoint of leadwire ingress of the device side terminal pins 142 a through142 d of the hermetic feedthrough 132. The embodiment shown in FIG. 39Bpositions the MLCC chip capacitor 210 closer to the point of leadwireingress of the device side terminal pin 142 in comparison with thepositioning of MLCC chip capacitors 210 a through 210 d to the ingressof the device side terminal pins 142 a through 142 d of FIG. 39. Theingress of the device side terminal pin 142 is also the point of ingressof undesirable EMI signals that may be picked up on an implanted lead.Having the MLCC chip capacitors as close as possible to the ingress ofthe device side terminal pin 142 of the hermetic feedthrough 132 isdesirable since at this ingress point the inductance or inductive loopinside the device is reduced. This helps to prevent the so-called“genie-in-the-bottle” effect wherein, once EMI is inside the AIMDhousing, it can cross-couple, re-radiate or couple through antennaaction to sensitive electronic AIMD circuits thereby causing disruptionin device therapy delivery. At MRI RF-pulse frequencies this is not aparticular concern since, for a 1.5 T scanner, the RF-pulse frequency is64 MHz. The wavelength of a 64 MHz signal is so long that it really doesnot effectively re-radiate once inside an AIMD housing. However, if theMRI filter MLCC chip capacitor 210 is also to be used as a broadbandlowpass filter, for example, where it must filter out very highfrequency signals above 1 GHz, such as those signals from cellulartelephones, then it is desirable to have the MLCC chip capacitor 210 asclose as possible to the point of leadwire ingress. Using an MLCC chipcapacitor for both diverting MRI RF-pulse frequencies and also as abroadband lowpass filter means that one desirably places the MLCC chipcapacitor as close as possible to the point of leadwire ingress. This isspecifically shown in FIG. 19 with MLCC chip capacitors 140′, which ofcourse, can be MLCC chip capacitors 210 in accordance with the presentinvention. One is also referred to FIG. 54, which places the MLCC chipcapacitors 210 a and 210 b directly at the point of leadwire ingressinto an AIMD housing, where the MLCC chip capacitors 210 a and 210 b areeach connected to a terminal pin (142 a and 142 b respectively) and tothe gold braze 152′ of the ferrule 134, thereby providing the lowestimpedance connection possible. Mounting MLCC chip capacitors directly atthe point of leadwire ingress is further taught by U.S. Pat. Nos.5,650,759 and 5,896,267, the contents of which are fully incorporatedherein by these references.

FIG. 39C illustrates the electrical schematic of FIG. 39B.

FIG. 40 illustrates an alternative embodiment to FIG. 39. Similar toFIG. 39, an AIMD circuit board and MLCC chip capacitors 210 a through210 d are shown; however, in the embodiment of FIG. 40, the groundcircuit trace 182 does not require an RF conductor such as the RFgrounding strap 264 to the AIMD housing. Instead, a shielded conduitassembly 266 is attached to the ferrule of the hermetic terminal (notshown). This shielded conduit 266 is grounded with a strap 268 which isconnected to the ground circuit trace 182. This type of EMI shieldedconduit assembly is more thoroughly described in U.S. Pat. No. 8,095,224to Truex et al., the content of which is fully incorporated herein bythis reference.

FIG. 41 shows a cross-sectional view of a flexible circuit board 270,which can also be a flex cable. The flexible circuit board 270 isattached on the left-hand side using a ball grid array (BGA) typeattachment 151. BGA attachment 151 is further connected to a terminalpin 142 that passes through a hermetic feedthrough 132 (not shown) of anAIMD. These types of flexible circuit boards, circuit traces orsubstrates are also described in the incorporated U.S. Pat. No.8,095,224 to Truex et al.

FIG. 42 shows a sectional view generally taken from section 42-42 ofFIG. 41 and shows the conductive circuit traces 178 a through 178 d.

FIG. 43 illustrates a sectional view generally taken from section 43-43of FIG. 41 and shows an optional embodiment wherein a ground circuittrace 182 is a ground circuit shield, the ground circuit tracesurrounding the four circuit traces 178 a through 178 d.

FIG. 44 is a sectional view taken generally from section 44-44 of FIG.41 and illustrates shield layers 272 a, 272 b. These shield layers 272a, 272 b are designed to surround each of the circuit trace layers 178as previously described in FIG. 42 or 43. These shields 272 a, 272 b arenot absolutely required, but greatly assist in preventing re-radiationof electromagnetic interference inside of the AIMD housing 124. Thisre-radiation of EMI can be very dangerous as it can couple to sensitiveAIMD circuits and disrupt the proper functioning of the AIMD.

FIG. 45 illustrates an embodiment in which the circuit traces 178 athrough 178 d of FIGS. 41 through 44 are connected to a circuit board270 or a circuit board substrate. Electrical attachments 274 are made toactive circuit traces and in turn to a multi-element diverterflat-through capacitor 210″. This three-terminal flat-through capacitor210″ is very similar to flat-through capacitor 140″ previously describedin FIGS. 17 and 18 except that the flat-through capacitor of FIG. 45 hasfour capacitors embedded in a single structure. Flat-through capacitor210″ may replace the individual MLCC chip capacitors 210 a through 210 dof FIGS. 39 and 40.

FIG. 46 shows a top view of the diverter flat-through capacitor 210″ ofFIG. 45.

FIG. 47 is a sectional view taken generally from section 47-47 of FIG.45 and shows the active electrode plates 212 of the flat-throughcapacitor 210″ of FIG. 45.

FIG. 48 is a sectional view taken generally from section 48-48 of FIG.45 and shows the ground electrode plate 214 of the flat-throughcapacitor 210″ of FIG. 45.

Accordingly, regarding the foregoing, it is appreciated that the presentapplication addresses the problems created when an MRI radio frequency(RF) pulse field couples to an implanted lead in such a way thatelectromagnetic forces (EMFs), voltages and current are induced in saidimplanted lead. The amount of RF energy that is induced is related to anumber of complex factors, but in general, is dependent upon the localelectric field that is tangent to the implanted lead and the integralelectric field strength along the implanted lead. In certain situations,these EMFs can cause currents to flow into the distal electrodes of theimplanted lead or at the point at which the electrode interfaces withbody tissue. It has been documented that, when RF current becomesexcessive, overheating of the implanted lead or its associatedelectrodes in contact with body tissue can occur. Consequently,overheating of the body tissue interfacing with the implanted leadelectrodes can also occur, and subsequently potentially causesubstantial body tissue damage. There have been cases of damage tocardiac tissue due to overheated electrodes, wherein the damage causedresulted in loss of capture of cardiac pacemaking pulses. Furthermore,with respect to neurostimulators, neurological tissue damage severeenough to result in brain damage or multiple limb amputations have alsobeen documented.

The present invention relates generally to methods and apparatus forredirecting RF energy to locations other than the distal tipelectrode-to-tissue interface. In addition, the present inventionprovides electromagnetic interference (EMI) protection to sensitiveactive implantable medical device (AIMD) electronics. The redirection ofthis RF energy is generally achieved by the use of frequency selectivedevices, such as inductors, capacitors and filtered networks. Asdescribed in U.S. Pat. No. 7,689,288, to Stevenson et al., the contentof which is fully incorporated herein by this reference, filtered energydissipation networks can range from a single capacitor, such as afeedthrough capacitor, to more complex filters that may include L-Ctraps and/or L-C bandstop filters co-operating in various ways with C,L, Pi (π), T or n-element lowpass filters. In general, this isaccomplished through frequency selective lowpass filters or seriesresonant L-C trap filters, wherein the RF energy can be redirected toanother surface or is converted to heat. In all of the above describedfrequency selective networks, it is the capacitor(s) (co-operating withother circuit elements) which diverts RF energy from an implantable leadto the conductive housing 124 of an AIMD. The relatively large surfacearea of the AIMD housing 124 acts as an energy dissipating surface (EDS)wherein a significant amount of the MRI energy can be harmlesslydissipated without significant temperature rise. However, the lowpassfilter, also known as diverter capacitor elements, must be designed tohandle a very high amount of RF current and power. Accordingly, thecapacitor's internal resistive or real losses known as equivalent seriesresistance (ESR) must be kept quite low. The present application isdirected to various embodiments of MRI diverter capacitor designs thatminimize the diverter capacitor's equivalent series resistance (ESR). Inaddition, the capacitor is also designed to direct heat to relativelylarge surface area heat dissipation surfaces, thereby creating anefficient heat removal system. These high RF power/low ESR divertercapacitors are an important feature of the filter network of the presentinvention for diverting induced RF energy from an implanted lead to anenergy dissipating surface, particularly a conductive housing 124 of anAIMD.

While these implantable lead systems are generally associated withAIMDs, such as cardiac pacemakers, cardioverter defibrillators,neurostimulators and the like, the present invention can also beincorporated into external devices, such as external pacemakers,externally worn neurostimulators (such as pain control spinal cordstimulators), catheters, probes, temporary external devices, temporarilyimplanted active devices and the like. It will be shown that for a givengeometry constraint, a preferred means of reducing the divertercapacitor's ESR is to select the most ideal dielectric type so that itsdielectric loss tangent (dielectric losses) is insignificant at the MRIRF-pulse frequency(ies). Of particular importance in the presentinvention is selection of a capacitor dielectric with the properdielectric constant (k) value. The preferred capacitor dielectric willhave a k of a sufficiently low value to thereby increase the number ofactive and ground electrode plates in the capacitor. This design featuredramatically reduces the ohmic losses in the capacitor at highfrequency. Therefore, to accomplish a relatively high electrode platecount, a low k capacitor dielectric is used. A non-limiting example ofone such dielectric material is an ElA standard, Class I dielectricmaterial, C0G, which is also known as NP0(negative-positive-zero)/(refer to EIA Standard ANSI/EIA-198-1-F-2002).Some low k capacitors may have a dielectric material having a k<1,000.Alternatively, some low k capacitors may have a dielectric materialhaving a mid k value, such as 400 to 700. Additionally, some low kcapacitors may have a dielectric material having a k<200. Some low kcapacitors may also have a dielectric material having a k<100.

In general, at first glance, using an EIA Class I dielectric iscounterintuitive. For example, consider a typical X7R MLCC chipcapacitor dielectric, with a dielectric constant of around 2,500. Withsuch a high efficiency dielectric material, which has a relatively highdielectric constant, it is possible to build, for example, a 1,000picofarad filter capacitor with two to four electrode plates. Nowconsider using an EIA Class 1 C0G dielectric, wherein the dielectricconstant is less than 100. A typical capacitor comprising the C0Gdielectric material generally requires greater than 20 or even 40electrode plates to achieve the same capacitance value as the X7Rcapacitor. The benefit of incorporating a C0G dielectric material withinthe capacitor design is generally a reduction of the capacitor's ESR atMRI RF-pulse frequencies. If designed properly, for example, designingthe capacitor with an appropriate number of electrode plates, the RFenergy heat that is produced when positioned within an MRI scanner canbe significantly reduced such that the heat resulting from RF energydoes not pose harm to biological tissue.

Hence, as disclosed above, one purpose of the low ESR diverter capacitoris to draw MRI induced RF energy out of the implanted lead and redirectsaid RF energy to the AIMD housing. Such low ESR capacitors have theeffect of reducing the RF energy that reaches the distal tip electrodeor its interface with body tissue. By redirecting said RF energy tolocations at a point distant from the distal electrodes, ideally theAIMD housing, this minimizes or eliminates hazards associated withoverheating of said distal electrodes during diagnostic procedures, suchas MRI. Another purpose of these low ESR diverter capacitors and relatedlowpass filter circuits is to provide electromagnetic interference (EMI)filtering in order to protect sensitive AIMD electronic circuits frommalfunctioning in the presence of MRI RF noise.

For maximum RF energy transfer out of the lead, frequency selectivediverter circuits are needed to decouple, and transfer energy inducedonto implanted leads from the MRI RF-pulse field to an energydissipating surface. Importantly, while decoupling and transferring suchenergy, it is extremely important that the diverter circuits do notthemselves overheat thereby creating hot spots on the AIMD housing,which can damage biological tissue, such as, in a pacemaker pectoralpocket. Recent experiments by the inventors resulted in temperaturerises from 4° C. to 10° C. on a pacemaker housing directly over thelocation of the feedthrough capacitor during a 4 watt/kilogram MRI scan.In general, prior art MLCC chip capacitors are really not indicated forhigh power RF applications. The reason for this is that the impedance(capacitive reactance) drops so low that extremely high RF currents endup flowing through the MLCC chip capacitor's electrode plates. During a4 watt/kilogram MRI scan where 16 to 20 volts may be induced at the AIMDinput, the diverter MLCC chip capacitor may be handling anywhere from0.5 amp to 4 amps of RF current. If the ESR of the MLCC chip capacitor,for example, is 0.5 ohm and the MLCC chip capacitor is diverting 2 amps,then the I²R loss is on the order of 2 wafts. Two watts of dissipationon this small MLCC chip capacitor component causes the MLCC chipcapacitor to overheat significantly. The present invention resolvesthese issues and provides other related advantages.

In summary, the RF diverting circuits, in general, conduct MRI inducedRF energy from the lead or its associated leadwires to an EDS such asthe housing 124 of the AIMD. The design of the diverter circuit is veryimportant. First of all, the diverter circuit should appear as a verylow impedance at MRI RF frequencies such that a maximum amount of RFenergy is diverted from the implantable lead to the EDS. In addition, itis also desirable that the diverter capacitor element be designed suchthat it does not overheat.

The mounting location of the diverter capacitor within an AIMD is alsotypically constrained by proper EMI design practices. Generally, EMIfilters are designed such that undesirable RF energy is diverted at thepoint of leadwire ingress to the AIMD housing, instead of letting theEMI inside the AIMD housing and then trying to filter said EMI furtherdownstream in the AIMD circuit path, for example, filtering at aninternal circuit board instead of at leadwire ingress. In an embodiment,at least one of the low ESR diverter MLCC chip capacitors of the presentapplication is mounted directly to the multi-pin hermetic feedthrough ofthe AIMD. This is an ideal location both to divert RF energy before itcan enter the AIMD housing and this is also optimal for heat conductionand dissipation. Even with low ESR, the diverter MLCC chip capacitorwill still be dissipating a significant amount of energy. This means,even with low ESR, the diverter MLCC chip capacitor is creating heatwhich must be conducted or convected away so that a hot spot does notoccur on the AIMD housing at or near the filter capacitor. Therefore, bydiverting both the RF energy and heat to the relatively large surfacearea of the housing of the AIMD, the MRI RF energy can be dissipatedwith only a small temperature rise, which does not adversely affect bodytissue.

It is noted that the general principle of placing a primary filtercapacitor (energy diverter) at the point of leadwire ingress in the AIMDhousing is generally the preferred EMI design practice. For relativelylow frequencies, such as an MRI RF-pulse frequency of 64 MHz, it isperfectly acceptable, however, to place the primary diverter filtercapacitor on a circuit board remote from the hermetic feedthroughotherwise known as the point of leadwire ingress.

FIG. 49 illustrates a family of lowpass filters, which is very similarto the family of lowpass filters described in FIG. 37. The lowpassfilters of FIG. 49 are also known as EMI filters, meaning that theyallow low frequencies to pass, but provide a substantial amount ofattenuation at higher frequencies. As previously disclosed, the lowpassfilters 260 of FIG. 37 incorporate a variety of capacitor designsranging from a simple MLCC chip capacitor “C” to a three-terminal“feedthrough filter capacitor-FTC”. These diverter capacitors can becombined in various ways with inductors to form “L”, “reverse L”, “T”,“Pi” (t), “LL”, “reverse LL” or “n” element lowpass filters. As can beseen in FIG. 49, there is a capacitor element 210′ in every one of thecircuits that is directed towards the implantable lead electrode (bodyfluid side). The conduction path is from the electrode of theimplantable lead, which is in contact with biological tissue, along theconductor of said implantable lead through the hermetic feedthrough ofthe AIMD along the feedthrough terminal pin directly to the capacitor210′. In accordance with the present invention, the capacitor 210′ is ahigh RF power, low ESR handling capacitor so that the capacitor 210′ andthe AIMD will not overheat in an MRI environment. One will also notethat the n-element filter has been revised so that there is no longer aninductor directed toward the implantable lead electrode. The version ofthe LL filter, with the inductor directed to the implantable leadelectrode has also been eliminated. In addition, the version of thetwo-element or L filter, with the inductor toward the implantable leadelectrode has also been eliminated. These elements are eliminatedbecause, in the present invention, it is very important that the primaryhigh-power RF handling capacitor have a direct connection from itsactive electrode plates through the hermetic feedthrough to the one ormore electrodes of the implantable lead.

Referring once again to FIG. 49, for the n-element, LL and Pi (π)filters, one can see that there are two capacitors 210′ and 140separated by an inductor. In the present invention, it is critical thatcapacitor 210′ have an ESR<0.5 ohm at the MRI RF-pulse frequency and bemade with a dielectric material having a dielectric constant k<1,000.This is so that it the capacitor 210′ can have a high electrode platecount and a very low equivalent series resistance at MRI pulsefrequencies. The capacitor element 140 can be constructed of a low ESRconstruction the same as capacitor 210′ or capacitor element 140 canalternatively be constructed as prior art filter capacitors aretypically constructed and that is with conventional ceramic dielectricshaving a k>1,000. Another way of looking at this is that the firstcapacitor directed toward the implanted electrode is the work horse andis going to do the bulk of the diverting of RF energy from the lead,diverting it to the AIMD housing where the energy and or heat can bedissipated over a large surface area.

As a point of reference, the first EMI filter ever designed for anactive implantable medical device was in the mid-1970s for the XytronMedtronic pacemaker. These were unipolar feedthrough capacitor EMIfilters that had a k>1,200. The principle designer on this filter designproject was Robert Stevenson, one of the co-inventors herein. The nextEMI filter to be designed for cardiac pacemaker was in 1979 for a St.Jude pacemaker. Robert Stevenson worked with St. Jude Vice PresidentBuehl Truex to design in this filter, which generally had a k>2,200. Theinventors herein have spent their entire careers designing EMI filtersfor a variety of applications, including AIMD applications. This issignificant in that there has never been a case where the primarypassive EMI Iowpass filter (the work horse filter) had a k<1,200. Inaddition, the inventors have either been asked to bid, have been awareof, or have cross-sectioned and analyzed explants of othermanufacturer's EMI filters and have found the same thing to be true andthat is, prior art EMI filters have consistently been built around adielectric structure that has a k of at least 1,200. For the last 30years, almost all primary EMI filters (the work horse filter) have beendesigned with a k of greater than 1,200. There are several reasons whythe industry has always designed EMI filters having a k of about 1,200(and generally above 2,00 to 2,200). The first important reason is thatactive implantable medical devices must be very small in size and verylow in weight. Another consideration is cost. By using a high kdielectric, one needs fewer electrode plates and can build the capacitormuch thinner and in a much smaller overall volume or footprint. This isideal for all AIMDs, again, where size and weight are critical. Untilthe MRI application came along, on which this patent focuses, it wasnever contemplated to do what is completely counterintuitive and that isto use a low k capacitor for AIMD filtering.

The parent application claims primary passive diverter capacitors (workhorse capacitors) having k<200. There is also a general reason for thisand that is that the major material suppliers in the ceramic dielectricindustries, such as Ferro, typically offer dielectrics either above1,200 k or below 200 k. As previously disclosed, the dielectrics below200 k are known as Class 1 dielectrics. These Class 1 dielectrics findbroad application in military and space applications, however, havenever been used for the primary EMI lowpass filter capacitor for an AIMDuntil now. There is a vast desert in terms of material supply in thedielectrics industry in that there are almost no suppliers of dielectricmaterials having k between 200 k and 1,000 k. There are a couple ofspecialty ceramic powder manufacturers, one of which is Dimat, Inc.Dimat offers a range of specialty dielectrics, including an N2200, whichhas a dielectric constant of 250; an N3300, which has a dielectricconstant of 400; an N4700, which has a dielectric constant of 600; and,an N5250, which has a dielectric constant of 700. There is also anothercompany called MRA Materials, which offers a dielectric with a k of 485and also a dielectric with a k of 600. Nevertheless, none of thespecialty or niche dielectrics companies have ever used or suggested useof such low k dielectric materials for a primary lowpass EMI filter foran AIMD. The present application teaches and claims that the primary EMIfilter capacitor, which is directly connected through wiring to animplantable lead conductor with distal electrodes, comprises a k<1,000.There is a practical reason for this. In some cases, the capacitancevalue can be considerably high, such as 1,800-pF. Building thiscapacitor out of a common commercially available dielectric, such as NP0(having a k of 90) results in a capacitor that has so many electrodeplates that it is often too thick to fit into a cardiac pacemaker.Accordingly, the inventors developed a mid k (intermediate) dielectric(between 200 k and 1,000 k), which presents an ideal tradeoff betweenvolumetric efficiency, a lower k, a higher number of electrode platesand, correspondingly, an ESR of less than 0.5 ohm that will meet all ofthe design criteria, including small in size, low in weight and low incost while effectively filtering.

In the embodiments herein, it is possible to split the primarycapacitance, the primary capacitance comprising a primary diverterlowpass filter capacitor, which is the work horse capacitor of the AIMD,by breaking up said primary capacitance into two areas. Referring toFIG. 37, shown is a primary capacitance broken up using two differentcapacitors, for example but not limited to, a feedthrough filtercapacitor (FTC) 210′ and a board mounted capacitor MLCC chip capacitor210. In a preferred functional primary capacitance design, the exemplaryfirst capacitor 210′ has a dielectric constant of less than 1,000 andeven preferably less than 200. For example, for a needed overallfunctional primary capacitance value of 1,800-pF, the high-energy, lowESR first capacitor 210′ can be 800-pF and the second board mountedcapacitor 210 can be 1,000-pF. It is noted that the exemplary secondboard mounted capacitor 210 can be conventional technology with adielectric constant above 1,000. Hence, the first capacitor 210′ and thesecond board capacitor 210 add up in parallel to provide 1,800-pF, whichis the functional primary capacitance design goal. The advantage offunctionally designing primary capacitance in this way is that the firstcapacitor (FTC) 210′ is thinner, thereby facilitating packaging of boththe first capacitor and the AIMD circuit board. The capacitance valuesof 800-pF and 1,000-pF are chosen at random and are not necessarilyrepresentative of any particular functional primary capacitance design.In other words, the first capacitor 210′ can have a capacitance of200-pF and the board capacitor 210 can have a capacitance of 1,600-pF.Accordingly, a functional primary capacitance design comprises a firstcapacitor and one or more additional capacitors, the first capacitorcomprising a first capacitance value and a dielectric material havingk<1,000, and the one or more additional capacitors each comprising anadditional capacitance value such that the sum of the first capacitancevalue and the additional capacitance values achieve a desired overallfunctional primary capacitance value. Furthermore, the capacitance valueof the first capacitor and the capacitance value of the one or moreadditional capacitors may comprise any capacitance value in any valuecombination to achieve the desired overall functional primarycapacitance value.

In summary, a primary filter capacitor (that is, a work horse filtercapacitor) having a dielectric constant of less than 1,000 has neverbeen built for use in AIMDs having a direct connection to the conductorof an implantable lead, the implantable lead having an electrode incontact with body tissues. As this application teaches, one of thereasons for this is that designing a capacitor with a dielectricconstant of less than 1,000 is completely counterintuitive forincorporation into AIMDs, as such capacitors require high number ofelectrode plates typically making such low k capacitors too big forAIMDs. Moreover, it is only with the advent of MRI conditional AIMDsystems and implantable leads and the recent discovery that a primaryfilter capacitor itself can substantially overheat during MRI scanning,causing the housing 124 of an AIMD implanted in a pectoral pocket toexcessively overheat such that the patient can actually feel a burningdiscomfort in the pectoral area of the chest, that primary filtercapacitors with a k<1,000 have become an attractive filtering designsolution. While dielectric constant capacitors (k<1,000) require a highnumber of electrode plates for the ESR of the capacitor to besufficiently low such that when the capacitor diverts RF energy (up to 6amps) at MRI RF frequencies, the capacitor itself will not overheat, thepresent application teaches embodiments having sufficient number ofelectrode plates to reduce the electrode resistance of the capacitor incombination with a dielectric material having a dielectric constantk<1,000 such that the primary filter capacitor (the working horsecapacitor) alone or in combination with one or more additionalcapacitors enables low ESR. As the ESR of a capacitor at high frequencyis primarily an ohmic loss, and assuming all other electricalconnections are solid, the ESR essentially comprises only the resistanceof the electrode plates. Increasing the number of electrode platessignificantly reduces ESR of low k capacitors. Dielectric constantselection of the dielectric material of the capacitor in combinationwith the number of electrode plates provides for overall functionalprimary capacitance value.

In the embodiments herein, the goal is to drop ESR substantially so thatinsignificant heat is produced by the filter capacitor itself and undueundesirable AIMD implant pocket heating does not occur. The FDA and theindustry generally limit implant pocket heating to about 4° C. It hasbeen demonstrated through experiments by the inventors that thecombination of overheating of prior art primary lowpass filtercapacitors with a k greater than 1,200 can by themselves result in theAIMD housing and the corresponding human pocket overheatingsignificantly above 4° C. The embodiments disclosed herein resolves suchheating problems among other related advantages.

Referring once again to FIG. 37, noted is a variation between thecircuit diagrams of the “LL” and “reverse LL” as compared to the “L” and“reverse L”. Referring to the LL filter, one can see that there is acapacitor 210 to the left of the inductor on the left-hand side circuitdiagram. For the reverse LL, there is an inductor to the left of acapacitor 210 on the right-hand side circuit diagram. Referring to the Lfilter, one can see that the inductor is to the left of the capacitor210 on the left-hand side circuit diagram (instead of the capacitor 210being to the left of the inductor as shown by the LL circuit diagram).Similarly, for the reverse L filter, the capacitor 210 is to the left ofthe inductor on the right-hand side circuit diagram (instead of theinductor being to the left of the capacitor 210 as shown by the reverseLL circuit diagram). FIG. 37 illustrates that there is really noindustry standard on what constitutes a reverse L or a reverse LLfilter. In fact, when manufactured, as such filters can be installed bythe user in either direction. As such, FIG. 49 illustrates a reverse Lfilter and a reverse LL filter both ways to emphasize that there reallyis no industry standard between the terms LL and reverse LL or L andreverse L. Hence, the reference in the claims to the LL, the reverse LL,the L and the reverse L filters refer to the specific electricalschematic shown in FIGS. 37 and 49 as well as in other detailedschematic diagrams herein.

Referring once again to FIG. 49, one will see that for a single elementcapacitor, said single element capacitor can be a two-terminal device“C” such as an MLCC chip capacitor or a three-terminal device “FTC” suchas a feedthrough filter capacitor. It is understood by those skilled inthe art that any of the capacitors 210′ shown in FIG. 49, can betwo-terminal capacitors “C” or three-terminal capacitors “FTC”, whereinthe two-terminal capacitors may comprise one of an MLCC chip capacitor,an X2Y attenuator, or combinations thereof; and wherein thethree-terminal capacitor may comprise one of a feedthrough filtercapacitor, an X2Y attenuator, a flat-through capacitor or combinationsthereof. It is noted that X2Y attenuators comprise both two-terminal andthree-terminal design configurations.

Referring once again to FIG. 49, one can see that the attenuation versusfrequency insertion loss curve for the three-terminal single elementfeedthrough filter capacitor “FTC” does not have a significant resonantdip at high frequencies. However, when one refers to the insertion losscurve for a single element two-terminal MLCC chip capacitor “C”, one cansee that the single element two-terminal MLCC chip capacitor has asignificant resonant dip at high frequencies shown as self-resonantfrequencies fr. Such self-resonant frequencies fr of the MLCC chipcapacitor is due to significant equivalent series inductance 204 asshown in the MLCC chip capacitor equivalent circuit diagram of FIG. 25.When a capacitor has equivalent series inductance, there is always goingto be some frequency at which the capacitive reactance is equal andopposite to the inductive reactance. This is known as the self-resonantfrequency of the capacitor. Observable in FIG. 49 is an insertion losspeak at the capacitor's self-resonant frequency fr. The two-terminalsingle element MLCC chip capacitor insertion loss versus frequency curvegoes to infinity if it were not for the MLCC chip capacitor's equivalentseries resistance. In other words, the MLCC chip capacitor has infiniteattenuation in dB if not for the capacitor's equivalent seriesresistance (ESR). The problem of a decreasing insertion loss of the MLCCchip capacitor occurs at frequencies above its self-resonant frequencyf_(r). At higher frequencies above a self-resonant frequency, theinductive reactance becomes increasingly dominant, which undesirablyreduces the filter attenuation in dB. Well mounted feedthrough filtercapacitors tend to have essentially zero equivalent series inductance204 as shown in FIG. 25 and therefore have a more ideal filterattenuation versus frequency insertion loss curve.

FIG. 49A reads on FIG. 39 and FIG. 39A. In FIG. 39, disclosed is thatone can split up the functional primary filter capacitance of an AIMDinto, for example, a feedthrough filter capacitor FTC 210′ and aboard-mounted capacitor MLCC chip capacitor 210 a. Referring to FIG.49A, the schematic diagram illustrates an exemplary embodiment of an FTC210′ in accordance with the present invention having a k<1,000 andextremely low ESR properties (an ESR of <2 ohms at the MRI RF-pulsefrequency) in parallel with a board-mounted capacitor MLCC chipcapacitor 210 (or 140′). The MLCC chip capacitor 210 (or 140′), can alsohave a k<1,000 (embodiment 210) in accordance with the presentinvention, or can have a k<200 (embodiment 210), or can be a prior artMLCC chip capacitor having a k>1,000 (embodiment 140′). Also shown inFIG. 49A is the composite insertion loss curve of the FTC 210′ inparallel with the MLCC chip capacitor 210 (or 140′). The dashed line(labelled MLCC ONLY) represents the effect on attenuation as a functionof frequency if the filter comprised only an MLCC chip capacitor. Onecan see that the attenuation of a filter having only an MLCC chipcapacitor reaches a maximum and then degrades at higher frequencies.With the low k feedthrough filter capacitor FTC 210′, which aspreviously disclosed has zero series inductance at high frequencies, onecan see that the attenuation picks up (lifts up) the degradation andinsertion loss that occurs from the MLCC chip capacitor only (in otherwords, improves attenuation at the high frequencies); hence, splittingup the functional primary filter capacitance of the filter between theFTC 210′ and the MLCC chip capacitor 210 (or 140′) yields an overallcombined broadband lowpass filter attenuation performance which ispreferred for AIMD EMI and MRI filters, as such filters provideelectromagnetic interference (EMI) protection to sensitive active AIMDelectronics and also handle RF energy or heat induced in an AIMD leadfrom an external RF field at a selected MRI frequency or a range of MRIfrequencies.

Referring back again to FIG. 49, one can see that each one of thelowpass filter circuits has a phantom inductor L′ drawn with dashedlines. The phantom inductor L′ is included in order to acknowledge thatall conductors have some amount of series inductance and that the amountof inductance is in series between the primary work horse capacitor (inthe example FTC 210′) and the distal lead conductor electrode. Theembodiments of the present application targets such series inductancesso that said series inductance L′ is kept as low as possible (as closeto zero as practical). If series inductance is too large, then a largeinductive reactance occurs at MRI RF-pulse frequencies, thereby reducingthe amount of energy that can be pulled from the lead. In other words,it is desirable that the first thing connected to the implantable leadelectrode along the path of the implantable lead is the work horsecapacitor (such as the exemplary FTC 210′) so that said work horsecapacitor can draw maximal energy out of the implanted lead. It is alsocritical that the work horse capacitor be very low in ESR, so that saidwork horse capacitor does not overheat while drawing literally amps ofMRI induced energy out of the implanted lead. Many implantable leadsthemselves are made of spiraled or of coiled construction and some ofthese are insulated, while others are not insulated. The uninsulatedlead conductors tend to short together, particularly when going throughtortuous paths, such as bends in a venous system. Therefore, theparasitic conductance of the uninsulated leads will vary significantlydue to design and lead trajectory differences. As such, the phantominductors L′ of FIG. 49 are meant to acknowledge that, pending AIMDsystem and lead design, some parasitic inductance can be associated withthe direct connection of the primary work horse capacitor (for example,FTC 210′) and a distal electrode. In summary, it is particularlyimportant that the parasitic inductance be minimized from the point ofleadwire ingress into the AIMD housing, that is, from the point wherethe leadwire passes through the conductive pathway of the insulator ofthe hermetic feedthrough. It is also very important that there beinsignificant or very little parasitic inductance between the work horsecapacitor and that point of leadwire ingress into the device side of theAIMD, namely inside of the AIMD housing.

FIG. 50 illustrates that a high energy dissipating low ESR capacitor210′ can be used in combination with other circuits, such as bandstopfilter 258 and/or an L-C trap filter 262, the bandstop and the L-C trapfilters each consisting of a capacitor 140 or 210 and an inductor L.Again, the capacitor of the bandstop filter 258 and the capacitor of theL-C trap can be conventional prior art filter capacitors or can be low kcapacitors. Regardless, capacitor 2101 is the work horse capacitor andmust comprise very low in ESR in accordance with the present invention,in other words, must be a low k capacitor.

FIG. 51 and FIG. 52 illustrate an MLCC chip capacitor 210 that issimilar in its exterior appearance to the prior art MLCC chip capacitor140′ previously described in FIGS. 14 and 15. In accordance with thepresent invention, the MLCC chip capacitor 210 of FIGS. 51 and 52comprises a dielectric material having a k<1,000 and an ESR of <0.5 ohmat the MRI RF-pulse frequency(ies). Also, in accordance with the presentinvention, The MLCC chip capacitor 210 comprises a relatively highnumber of active electrode plates 144 and ground electrode plates 146compared to the prior art MLCC chip capacitor 140′ of FIGS. 14 and 15.

FIG. 53 is the electrical schematic of FIGS. 51 and 52 showing that theESR of MLCC chip capacitor 210 is less than 0.5 ohm.

FIG. 54 is a bipolar hermetic feedthrough having a metallic ferrule 134and two terminal pins 142 a and 142 b passing through the insulator 156in insulative relationship with the conductive ferrule 134. There aretwo MLCC chip capacitors 210 a and 210 b, as illustrated in FIGS. 51 and52, connected respectively to terminal pins 142 a and 142 b. The MLCCchip capacitors are shown attached to a gold braze 154 a, the gold brazehermetically sealing the insulator 156 to the ferrule 134 of thehermetic feedthrough so that an essentially oxide-free (oxide-resistant)and low resistance electrical connection is made. Such oxide-resistantelectrical connections are more thoroughly disclosed in U.S. Pat. No.6,765,779, the content of which is fully incorporated herein by thisreference. MLCC chip capacitors attached to a gold braze of a hermeticfeedthrough are also disclosed in U.S. Pat. No. 10,080,889, the contentof which is fully incorporated herein by this reference.

Referring now back to FIG. 19 of the present application, it iscontemplated that the MLCC chip capacitor 210 of FIGS. 51 and 52 canalso be mounted to a substrate 147 as shown in FIG. 19. Additionally,the MLCC chip capacitor 210 can be mounted on a circuit board. Moreover,the substrate and/or the circuit board can be mounted to the hermeticfeedthrough adjacent one of the ferrule 134, the insulator 156, or boththe ferrule and the insulator in accordance with the definition ofadjacent previously disclosed. Furthermore, such circuit boards andsubstrates can be mounted immediately adjacent the hermetic feedthrough,distant from the hermetic feedthrough or even at a remote location ofthe hermetic feedthrough. As defined herein, the remote location isstill inside of the AIMD housing, but located remotely from the hermeticterminal, including the feedthrough ferrule and/or insulator.

FIG. 55 is a schematic diagram of the bipolar filtered hermeticfeedthrough of FIG. 54.

FIG. 56 is similar to FIGS. 6 and 39 illustrating a breakawaycross-section of a typical AIMD, such as a cardiac pacemaker, exceptthat instead of a feedthrough capacitor (140 of FIG. 6 and 210′ of FIG.39) attached adjacent the ferrule 134 of the hermetic feedthrough, acircuit board having filter MLCC chip capacitors are attached to thehermetic feedthrough. As previously disclosed, prior art feedthroughcapacitors such as the feedthrough filter capacitor 140 of FIG. 6, andwhich are used for primary EMI filtering of AIMDs, have always beenbuilt from dielectric materials having k>1,000 k. The feedthrough filtercapacitor 210′ of FIG. 39 has a dielectric material having k<1,000.

Referring to FIG. 56, illustrated is a circuit board 130 similar to thecircuit board 130 previously illustrated in FIG. 39, however, in thiscase, each of the device side terminal pins 142 of the quad polarhermetic feedthrough 132 are attached to a respective MLCC chipcapacitor 210 a through 210 d. The MLCC chip capacitors 201 a through210 d are low ESR (low k MLCC chip capacitors having k<1,000) inaccordance with the teachings of FIGS. 51 and 52. The leadwires 136 athrough 136 d of the hermetic feedthrough 132 each connect on the deviceside terminal pin 142 to an active capacitor metallization 164 (notlabelled) of their respective low k MLCC chip capacitor 210 a through210 d. These extremely low ESR (low k) MLCC chip capacitors functionallydraw a great deal of RF energy and/or heat from an implanted lead whenin an MRI environment. It is important that this RF energy beefficiently dissipated to the AIMD housing 124, wherein the RF energycan be dissipated as RF energy and/or heat. As such, there is a lowinductance ground circuit trace 182, which provides a ground connectionto the ground capacitor metallization 166 (not labelled) of each MLCCchip capacitor 210 a through 210 d to each respective device sideterminal pin 142 of leadwires 136 a through 136 d. This efficientlydiverts RF energy from the leadwires 136 a through 136 d to the groundcircuit trace 182. There is also an optional RF grounding strap 264attached to ground circuit trace 182. The RF grounding strap 264 may beused to substantially reduce inductance making the filter circuit board130 more efficient for diverting the RF energy to the AIMD housing 124at high frequencies. The circuit trace may comprise may have increasedwidth commensurate with the connection pad to which the RF groundingstrap 264 is attached. The RF grounding strap may be substantially widecompared to its thickness. In an embodiment, the RF grounding strap maycomprise a width >4 times its thickness.

FIG. 56A is a schematic diagram of the primary work horse filter MLCCchip capacitors 210 a through 210 d illustrated in FIG. 56. Shown areeach one of the work horse low ESR filter MLCC chip capacitors 210 athrough 210 d in series with a parasitic inductance LP. This parasiticinductance L_(P) comprises the inductance of the leadwire, from thelength of the leadwire at the point of leadwire ingress, through thehermetic feedthrough, to the circuit board connection, to the MLCC chipcapacitor (the four MLCC chip capacitors 210 a through 210 d arerepresented in the schematic diagram of FIG. 56A). The parasiticinductance L_(P) also includes the inductance of the ground circuittrace 182 and the RF grounding strap 264. It is desirable to keep thisparasitic inductance LP as low as possible. That is why the groundcircuit traces 182 and the RF grounding strap 264 are relatively wide.It is also important to minimize the inductance of the device sendterminal pin 142 between the hermetic feedthrough and the active end(non-ground end) of the primary filter MLCC chip capacitors 210 athrough 210 d. This can be done by making the device end terminal pin142 shorter, larger in diameter, flat, rectangular or a combinationthereof.

Referring once again to FIG. 56, one can see that the leadwires 136 ofhermetic feedthrough 132 are directed to via holes in the multi-layercircuit board 130. The via hole of the multi-layer circuit board 130comprises a via hole metallization to which the active capacitormetallization 164 (on the left-hand side of the MLCC chip capacitors notlabelled) of the filter MLCC chip capacitors 210 a through 210 d isattached. The active metallization 164 provides electrical connection tothe active electrode plates of the MLCC chip capacitor. The device sideterminal pins 142 pass through the via holes in the multi-layer circuitboard 130 to the layers of said multi-layer circuit board, wherein thedevice side terminal pins 142 contact active circuit traces shown asdashed lines (hidden lines). Thus, the circuit from the body fluid sideleadwires 136 through the primary filter MLCC chip capacitors 210 athrough 210 d through the circuit traces of the multi-layer circuitboard 130 to the ground circuit trace 182, wherein the ground circuittrace 182 connects to other via holes (not shown), is completed. The notvia holes (not shown) connected to the ground circuit 182 are connectedto other AIMD electronics, such as an ASIC electronics chip or otherAIMD circuits.

FIG. 57 is very similar to FIG. 56 except that an overvoltage diodeprotection array 181 has been added. It is very common in the inputcircuitry of AIMDs to provide an overvoltage protection diode array 181mainly against the use of automatic external defibrillators (AEDs). AEDscan induce a very large high voltage pulse into implanted leads and thehigh voltage of such a pulse can be undesirably directed towardsensitive AIMD electronic circuits. Thus, the overvoltage protectiondiode array 181 provides high voltage overprotection for each one of thequad polar leads 136 a through 136 d to ground, which in FIG. 57 is theAIMD housing 124.

Overvoltage protection is better understood by referring to theschematic diagram of FIG. 58, which is representative of the AIMD systemof FIG. 57. One can see that there is a continuous electrical circuitconnection from the implantable lead electrode to the AIMD circuits.Leadwires 136 a through 136 d, the low ESR high RF-energy dissipatingcapacitors MLCC chip capacitors 210 a through 210 d of the presentinvention and a high voltage protection diode array 181 are continuouslyconnected. Each MLCC chip capacitor 210 a through 210 d remains the workhorse capacitor as the primary diverter of high frequency MRI RFenergy/heat to the AIMD housing 124. It is noted that the embodiment ofFIG. 57 illustrates the circuit ground path to the AIMD housing 124comprising an RF grounding strap 264. The overvoltage diode protectionarray 181 of FIG. 58, now part of the circuit between the implantablelead electrode and the AIMD circuits, is positioned on the left-handside of the MLCC chip capacitors 210 a through 210 d.

FIG. 59 is very similar to FIG. 58 except that the high voltageprotection diode array 181 is shown on the right-hand side of the lowESR capacitors MLCC chip capacitors 210 a through 210 d of the presentinvention. Since the high voltage protection diode array 181 is not inseries, but is in parallel with the low ESR capacitors, it is understoodby one of ordinary skill in the art that the low ESR MLCC chipcapacitors 219 a through 210 d can be placed anywhere along the lengthof the leadwires 136 a through 136 d. Regardless of where the highvoltage protection diode array 181 is positioned, it is understood thatthe low ESR capacitor of the present invention is always directlyconnected by way of continuous electrical circuit connections, such asthe circuit connections to the circuit pads of the circuit tracesillustrated in FIG. 57. Thus, a continuous electrical path between theAIMD circuits and the implantable lead electrode contactable tobiological cells through the leadwires of the hermetic feedthroughtherebetween is provided.

Referring once again to FIG. 58, one will notice that the diodes of theovervoltage protection diode array 181 are back-to-back so that saiddiodes can clamp and shunt a positive or a negative polarity pulse. ForAEDs, it is common for shocking pulses to be biphasic, meaning that theshocking pulse switches polarity. Therefore, it is common practice toorient the diodes of the overvoltage protection diode array 181back-to-back so that the diodes may shunt energy having both positiveand negative polarities. It is noted that the diodes of the overvoltageprotection diode array 181 must be positioned before or after theprimary EMI low ESR capacitor before placing any other electroniccomponents like electronic chips, ASIC chips, active filters or othersensitive electronics in this portion of the circuit path, as suchelectronic components are the very components that can be damaged by anovervoltage or can be interfered with by EMI. As a result, in general,such ‘sensitive’ AIMD electronic components are always positioneddownstream (to the right) of the circuits of FIG. 58 or 59.

FIG. 60 is an alternative diode connection for the circuit schematics ofFIGS. 58 and 59. FIG. 60 illustrates that instead of two discreteseparate diodes wired back-to-back, the diodes of an overvoltageprotection diode array 181 can be alternatively placed back-to-back inseries. Sometimes such back-to-back series diode arrays are calledTransorbs©. Ii is understood that, in general, the diodes of theovervoltage protection diode array 181 can be selected from the groupconsisting of a transient voltage suppressor, a varister, an avalanchediode or a Zener diode.

FIG. 61 is very similar to FIG. 56 except that the RF grounding strap264 has been replaced with a simple RF grounding leadwire 264′. An RFgrounding leadwire 264′ works okay at relatively low RF frequencies. Forexample, for a 1.5 Tesla scanner, the RF-pulse frequency is 64 MHz. Asscanners have evolved to higher and higher frequencies, the inductanceof such a small wire can become problematic. For example, there are manymodern scanners in the market operating at 3 Tesla, which means that theRF frequency is 128 MHz. The inductive reactance is equal to2×π×frequency×inductance. So, if the inductance is small and thefrequency is large, one can get a great deal of inductive reactancewhich makes the diversion of high frequency energy through the primarylow ESR chip capacitors 210 less efficient. Another way of saying thisis that you really don't want anything in the ground path that impedesdiverting the high frequency RF energy to the AIMD housing 124. One wayaround this (not shown) is to use multiple RF grounding leadwires 264′,thereby creating additional circuit paths to ground and reducing theinductance.

FIG. 62 is very similar to FIG. 61 except in this case, a groundingleadwire 264″ is routed directly from the ferrule 134 of the hermeticfeedthrough 132 to the ground circuit trace 182 of the AIMD circuitboard 130 (not labelled).

FIG. 63 and FIG. 64 are very similar to the prior art flat-through typefeedthrough capacitor of FIGS. 17 and 18. These flat-through typecapacitors are unique in that the circuit current must pass through theflat-through capacitor's own active electrode plates instead of througha feedthrough leadwire 136 extending through a metallized viaelectrically connecting the active electrode plates 144 as shown in thefeedthrough filter capacitors 140 of FIGS. 7-10. Regarding FIGS. 63 and64, the circuit current i₁ of the flat-through capacitor 210″ is shownentering the active electrode plates 144 as i_(1a) and exiting saidactive electrode plates as i_(1b).

FIG. 64A is the circuit diagram of the flat-through capacitor 210″ ofFIGS. 63 and 64. Illustrated is that the flat-through capacitor 210″ isa three-terminal filter capacitor. However, instead of having a leadwire136 going through the center of the three-terminal capacitor asillustrated in the schematic diagram of the feedthrough filter capacitor140 of FIG. 11, one actually has the active electrode plates 144 goingthrough the center of the three-terminal flat-through capacitor 210″.The circuit current (not shown) of FIG. 11 passes to the activeelectrodes plates 144 of a three-terminal feedthrough filter capacitorby way of the leadwire 136, while the circuit current 180 of theflat-through capacitor 210″ of FIG. 64A passes through the activeelectrode plate 144 itself. In accordance with the present invention,the capacitor dielectric of the flat-through capacitor 210″ has a kgreater than 0 but less than 1,000, k<1,000, and an ESR generally lessthan 0.5 ohm at an MRI RF-pulse frequency including an MRI RF-pulsefrequency of 64 MHz (1.5 T) and 128 MHz (3 T).

Referring once again to FIG. 63, one can see that the flat-throughcapacitor 210″ is installed on an AIMD circuit board 130 (not shown) alittle differently. Installation of the flat-through capacitor 210″ ofFIG. 63 require circuit traces 178 a and 178 b. Circuit traces 178 a and178 b are made on a circuit board substrate such that the endmetallizations of the flat-through capacitor 210″ can properly beattached, in other words, the circuit traces 178 a and 178 b of thecircuit board are positioned to accommodate a flat-through capacitorattachment. Such circuit traces are separated by an insulating area,that is, there is a break in the circuit trace, such that, when theflat-through capacitor 210″ is attached to the circuit traces 178 a and178 b, a circuit current i₁ can pass all the way through the activeelectrode plates 144 from the left-hand side of the flat-throughcapacitor, labelled ha, through the active electrode plates 144, to theright side of the flat-through capacitor, labelled ill). As shown, i₁ isgoing from the left-hand side to the right-hand side, but it isunderstood that i₁ can also pass through the active electrode plates inthe opposite direction, namely from the right-hand side to the left-handside of the flat-through capacitor 210″ depending on the AIMDtherapeutic algorithms.

Referring once again to FIG. 63, one can see that there is a groundconnection 182 a and 182 b. This ground connection is routed to the AIMDhousing 124.

Referring once again to FIG. 64A, the schematic diagram of theflat-through filter of FIGS. 63 and 64 shows that the circuit current i₁passes through the flat-through capacitor at an input terminal 178 a(terminal 1) and then exits the active capacitor electrode plates 144 atan output terminal 178 b (terminal 2). It is appreciated that theflat-through capacitor being a three-terminal device is symmetrical,meaning that the attachment of the flat-through capacitor 210″ to thecircuit can be reversed and still operates in the same fashion.Referring again to FIG. 63, it is noted that the left-hand side of theflat-through capacitor 210″ has been arbitrarily labelled as the bodyfluid side and the right-hand side as the device side. As previouslydisclosed, electromagnetic interference (EMI) can be coupled or radiatedto body fluid device side leads and electrodes and can undesirablyappear as an RF current ha at the input terminal 178 a (terminal 1) ofthe flat-through capacitor 210″; it is noted that i₁ also comprises lowfrequency therapeutic pacing pulses or biologic signals in addition toany EMI RF current. Such EMI passes through the active electrode plates144 of the flat-through capacitor 210″ and is continuously decoupledthrough capacitive filter action to the ground electrode plates 146(terminal 3). When the current i_(1b) exits at the device side terminal178 b (terminal 2), the EMI has been greatly attenuated (filtered) suchthat said EMI can no longer dangerously interfere with AIMD circuitry.As shown, the attenuated current i_(g) is diverted (filtered) to ground,which as shown is the ferrule 134 of the hermetic feedthrough 132 (notshown). This three-terminal filter behavior is very similar tofeedthrough filter capacitors, which are also three-terminal devices.The difference is that, for a feedthrough capacitor, circuit currentspass through a leadwire, such as leadwire 142 illustrated in the priorart feedthrough filter capacitors of FIGS. 7 to 10, while the circuitcurrents for flat-through capacitors flow through its own activeelectrode plates 144. Therefore, it is important that the activeelectrode plates 144 be robust and low in DC resistance, Typically, thismeans that a relatively large number of active electrode plates 144appears in parallel and interleaves between ground electrode plates 146.By having additional electrodes in parallel, one reduces the overallresistance to the flow of current, otherwise known as DC resistivity.

In accordance with the present invention, the embodiments, whichcomprise a first filter capacitor, meaning the first capacitor from thepoint of implanted leadwire ingress that EMI encounters, has a k greaterthan zero and less than one thousand, k<1,000. This is distinct and inmarked contrast to prior art filter devices, which generally havedielectric constants of k greater than 1,200, or 2,500, or even higher.By reducing the dielectric constant of the filter capacitor, an increasein the number of active electrode plates 144 and ground plates 146 isrequired in order to achieve an equivalent capacitance value and amountof filtering comparable to that of prior art high k, k>1,200 filtercapacitors. This makes the low k flat-through capacitors 210″, asillustrated in FIGS. 63 and 64, highly suitable for use in AIMDs, as thehigher number of active electrode plates 144 of such low k, k<1,000,flat-through capacitors 210″ reduce the DC resistance of said low kflat-through filter capacitors. It is noted that it is also importantthat the impedance of the active electrode plates 144 of the low kflat-through capacitors also be low. However, if the low k flat-throughcapacitors have inductance L as shown in FIG. 64A, the inductance Lshown aides in the EMI filtering because this inductance L is along thei₁ circuit path. It is noted that at high frequencies, such as EMI RFfrequencies, the inductive reactance is given by the equation XL=2πFL.This means that at high frequencies, the amount of inductance reactancebecomes very high thereby further impeding EMI from undesirably enteringfrom the body fluid side to the device side of an AIMD.

Referring once again to FIG. 64A, shown is that EMI can radiate across aflat-through capacitor. The potential for radiating EMI across aflat-through capacitor occurs at exceptionally high frequencies. At suchexceptionally high frequencies, EMI is not attenuated by theflat-through capacitor. Because such high frequency coupling only occursat very short-wave lengths, generally at microwave frequencies, andbecause the human body both reflects and absorbs microwave energy, theamount of EMI picked up by implanted leads is substantially degraded andessentially inconsequential. Accordingly, flat-through capacitors makean attractive alternative to MLCC chip capacitors as primary filtercapacitors, which can be extremely helpful for AIMDs having particularlysmall geometries. In summary, EMI can effectively be diverted by the lowk flat-through capacitor of the present application to an AIMD systemground (attenuated current i_(g)), the system ground being the ferrule134 (terminal 3) of the hermetic feedthrough, which is at the sameelectrical potential as the overall electromagnetic shield (housing) ofthe AIMD.

FIG. 64B is a top view of a tri-polar filter circuit board 130 havingthree flat-through capacitors 210″a, 210″b and 210″c or, alternatively,three MLCC chip capacitors 210 (not shown). FIG. 64B illustrates on theleft-hand side of each flat-through capacitor 210″, a circuit currenti_(1a) that enters at the input 178 a (terminal 1) of the flat-throughcapacitor 210″. The leadwire positioned at 178 a is cut off on thedevice side but is routed to implanted leadwires and the lead electrodes(not shown) on the body fluid side. On the right-hand side of theflat-through capacitors 210″, the output current ilb exits at output 178b (terminal 2), which is also connected to a leadwire inside the AIMD.The leadwire positioned at 178 b projects upwardly out of the hermeticfeedthrough. The leadwire layout and configuration is best understood byreviewing the cross-sectional view of FIG. 64C.

Referring once again to FIG. 64B, circuit current ha enters theflat-through capacitor 210″ on the left-hand side and freely passesthrough the flat-through capacitor exiting as circuit current i_(1b)because circuit current i_(1a)-i_(1b) comprises either biologic signalsor therapeutic pacing pulses, which are low frequency circuit currents.However, at high frequencies, such as EMI RF frequencies, circuitcurrent ha on the left-hand side 178 a (terminal 1) is of a relativelyhigh amplitude, therefore, as circuit current lib exits on theright-hand side 178 b (terminal 2) of the flat-through capacitor 210″,the EMI, which appears as an RF current, is substantially attenuatedbecause the flat-through capacitor 210″ acts as a filter capacitor athigh frequencies such as the EMI RF frequencies.

Referring now to FIG. 64C, one can see that on the body fluid side ofthe hermetic feedthrough, the circuit current i_(1a) flows toward thedevice side of the hermetic feedthrough through a terminal pin 142 a tothe input 178 a (terminal 1) of the flat-through capacitor 210″a. Thecircuit current ha then flows through the flat-through capacitor 210″aand exits at the output 178 b (terminal 2) of said flat-throughcapacitor as circuit current i_(1b). Circuit current i_(1b) then flowstoward the device side of the hermetic feedthrough through terminal pin142 a′. Circuit current i_(1b) is then routed to the AIMD electroniccircuits. The AIMD electronic circuits typically reside in or on an AIMDelectronic circuit board (not shown). Any undesirable RF currents, suchas an EMI RF current, are diverted (filtered) by the flat-throughcapacitor 210″ as attenuated current i_(g) to the AIMD system ground,such as ferrule 134, which is attached to the AIMD housing 124 (notshown). Referring once again to FIG. 64C, one will appreciate thatcircuit current i₁ can desirably contain therapeutic pacing pulses,which are being routed from the AIMD to implanted leads and distalelectrodes or circuit current i₁ can include biological sensingfrequencies, such as cardiac signals, which are being sensed by theinternal circuitry of the AIMD. In other words, circuit current i₁ canflow in either direction. In addition, circuit current i₁ canundesirably contain very high EMI RF currents, which can be dangerous,even life-threatening, to a patient as previously disclosed.

FIG. 64C further shows a method of grounding a filter circuit board,wherein the filter circuit board has at least one internal (oralternatively external) ground plate 161. The ground plate 161 of thefilter circuit board is connected to an AIMD system ground, which inFIG. 64C is the ferrule 134 (terminal 3) of a hermetic feedthrough 132(not labelled). In this exemplary embodiment, illustrated on theleft-hand side is a ground pin 142 gnd, which is gold brazed 165 (oralternatively laser welded 157, not shown) into the ferrule 134 of thehermetic feedthrough. The terminal pin 142 gnd is shown attached in ablind via of the ferrule 134. An alternative embodiment is shown on theright-hand size, wherein the terminal pin 142 gnd′ extends through a viain the ferrule 134 to a body fluid side and a device side. The terminalpin 142 gnd, 142 gnd′ of FIG. 6C comprises an oxide-resistant material(or may alternatively comprise an oxide-resistant outer layer, such asan oxide-resistant coating, plating, or cladding) such that a very lowimpedance electrical connection can be made both to the terminal pin andto various via hole connections to the at least one filter circuit boardground plate 161. Filter circuit board ground plate 161 is shownconnected to six (or can alternatively be connected to “n” number)flat-through capacitor grounds (exemplary grounds 182 a, 182 b are shownin FIG. 64B). Referring to FIG. 64B, one will appreciate that thegrounds 182 a, 182 b can be circuit board via holes or include circuittraces. What is important is that both the grounds 182 a and 182 b areconductively coupled through the circuit board via holes to the at leastone ground plate 161. This creates a multipoint grounding system, whichmakes flat-through capacitors very effective three-terminal filters foruse in AIMDs, including filter circuit boards connected to a hermeticfeedthrough of an AIMD that effectively filters EMI.

FIG. 64D is an isometric view of a quad polar flat-through capacitor210″. The quad polar flat-through capacitor 210″ is similar to theunipolar flat-through capacitor of FIG. 63, except in this case thereare four active electrode plates 144 (see FIG. 64E). As previouslydisclosed, circuit currents i₁ (i_(1a)-i_(1b)) pass through the activeelectrode plates of the quad polar flat-through capacitor of FIG. 64D.The quad polar flat-through capacitor of FIG. 64D also comprises acommon ground plate 146 (also illustrated in FIG. 64E). Referring onceagain to FIG. 64D, each of the active electrode plates 144 has an activetermination comprising active capacitor metallizations 164 a, 164 a′through 164 d,164 d′. The ground electrode plate 146 has an edgetermination comprising ground capacitor metallization 166 suitable forelectrical attachment to an AIMD system ground, for example, the ferrule134 of the hermetic feedthrough, which is attached to the housing 124 ofthe AIMD, the ferrule and the AIMD housing having the same electricalpotential as the system ground potential.

Referring once again to FIG. 63, one can see that there are groundconnection circuit traces 182 a and 182 b. These ground circuit tracesare routed to the AIMD housing 124.

FIG. 64F is a schematic electrical diagram of the quad polarflat-through capacitor 210″ of FIGS. 64D and 64E. The body fluid side isdepicted on the left-hand side showing that circuit currents i_(1a)entry, which then exits as current i_(1b) on the right-hand side, whichis the device side, to the AIMD circuits. When the circuit currenti_(1a) is an undesirable EMI RF current, i_(1b), is greatly attenuated(filtered). The filtering action of the flat-through filter capacitor210″ diverts any high-frequency EMI signals as an attenuated currenti_(g) to the AIMD system ground 124. The attenuated current i_(g) is adiverter current or a filtered current, wherein any undesirable or evendangerous EMI signals are diverted or filtered to ground where such EMIsignals are dissipated by the AIMD housing 124 as RF energy or heat.

FIG. 65A is a top view (looking down on the device side of the ferrule134) of the quad polar flat-through capacitor 210″ of FIG. 64Dedge-mounted in a tombstone position. The edge ground capacitormetallizations 166 (not labelled) are shown electrically connected to aterminal pin 142 gnd on the left-hand side and to an oxide-resistantarea 248, 250 on the right-hand side. These oxide-resistant groundconnections is further described in FIG. 65B. It is understood that theoxide-resistant area 248, 250 may comprise a pocket-pad, a pocket, apad, a metal addition or an ECA stripe. The ECA stripe is taught in U.S.provisional 62/979,600, the content of which is fully incorporatedherein by this reference. The oxide-resistant area 248, 250 may comprisea material selected from the group consisting of platinum, gold,tungsten, iridium, palladium, niobium, tantalum, ruthenium, rhodium,silver, osmium, and alloys or combinations thereof. The oxide-resistantmaterial of the ground terminal pins 182 gnd may further be selectedfrom the group consisting of platinum-based materials includingplatinum-rhodium, platinum-iridium, platinum-palladium, or platinum-goldand naturally occurring alloys such as platiniridium (platinum-iridium),iridiosmium and osmiridium (iridium-osmium). Furthermore, the electricalconnection material 152 can attach directly to the gold braze 154 a ofthe hermetic feedthrough thereby providing an oxide resistanceelectrical attachment.

The tombstone mounting position refers to a filter capacitor orientationin which the ground electrode plates and the active electrode plates ofthe filter capacitor are positioned perpendicular to the surfaces of theferrule and the insulator of the hermetic feedthrough. Typically, theground and active electrode plates of a filter capacitor are alignedparallel with the body fluid side and device side surfaces of theferrule and the insulator of the hermetic feedthrough (see FIGS. 7, 8,9, 10, 13, 34, 54, 64B, 64C, 70A, 70B, 71B, 71C, 72B, 72C, 73, 74A, 74B,74C, 75, 76, 77, 78, 79, 80, 82, 84, 85 of the present application). Incontrast, the tombstone mounting position positions the ground electrodeplates and the active electrode plates perpendicular to the body fluidside and device side surfaces of the ferrule and the insulator (seeFIGS. 65A, 65B, 65E, 65F, 65I, 65J, 65K, 65L, 65M, 65O, 65Q, 65R, 65S,65T, 70C and 70D of the present application). Referring specifically toFIG. 65A, illustrated is a device side surface 133 of the ferrule 134and a device side surface 135 of the insulator 156. The ground electrodeplates 146 and the active electrode plates 144 of the flat-throughcapacitor 210″ are positioned perpendicular in relation to ferrule andinsulator surfaces 133 and 135.

Further regarding FIG. 65A, electrical connections from the hermeticfeedthrough to the AIMD circuit board and/or the AIMD circuitry can bemade by one of a round wire such as 142 a of FIG. 65A′, a nail-headleadwire such as 142 b′ and 142 c′, a flat ribbon such as 142 d′ orcombinations thereof. These are only exemplary connection options, asthere are various other ways of connecting to an AIMD circuit boardand/or AIMD circuitry (not shown), including directly abutting thecircuit board to terminations and making a direct electrical connection.Also, a connection to flexible circuit boards or at least a portion of aflexible circuit board can be done. Any of the electrical connectionspreviously disclosed in U.S. Pat. No. 8,195,295 can also be incorporatedinto the embodiments of the present application. Accordingly, thecontent of U.S. Pat. No. 8,195,295 is fully incorporated herein by thisreference.

FIG. 65B is a cross-sectional view taken from section 65B-65B of FIG.65A. The insulator 156 of the hermetic feedthrough comprises variousfeedthrough conductive paths 129. For example, an embodiment on the farleft-hand side of the hermetic feedthrough illustrates a conductive pathcomprising a nail-head leadwire 142 a, which can alternatively be just aplain leadwire. Another embodiment to the right of far left-hand sideembodiment comprises a co-sintered past-filled via comprising a ceramicreinforced composite (CRMC) 185 and platinum caps 187. Next, to theright of the embodiment just disclosed is another a co-sinteredpast-filled via embodiment comprising a platinum core 187 surrounded bya CRMC outer layer 185. It is appreciated that, alternatively, theentire co-sintered via can comprise just an essentially pure co-sinteredplatinum paste-filled via without any CRMC. On the far right-hand sideis another co-sintered past-filled via embodiment comprising a dumbbellshape formed by the combination of the platinum 187 and the CRMC 185materials. The embodiments of the feedthrough conductive paths 129 ofthe hermetic feedthrough of FIG. 65B are exemplary only and may comprisevariations thereof. For example, the feedthrough conductive pathway 129may be selected from the group consisting of a terminal pin, a pin, aleadwire, a lead wire, a two-part pin, a lead conductor, a sinteredpaste-filled via, a co-sintered via, a co-sintered paste-filled via, aco-sintered via with one or more metallic inserts, or combinationsthereof. The feedthrough conductive pathway 129 may comprise the sameembodiment for all feedthrough conductive pathways of the hermeticfeedthrough, or alternatively may comprise at least one differentfeedthrough conductive pathway of the total feedthrough conductivepathways of the hermetic feedthrough.

Referring again to FIG. 65B, two methods of grounding the flat-throughcapacitor is shown. On the right-hand side, the electrical connectionmaterial 152 is shown attached to an oxide-resistant area 248, 250. Theoxide-resistant area may comprise a pocket, a pad (for example, a goldpocket or a gold pad), a metal addition or an ECA strip. Gold pocketsand gold pads are more thoroughly described in U.S. Pat. No. 10,350,421,the content of which is fully incorporated herein by this reference. Onthe left-hand side, the ground capacitor termination 166 of theflat-through capacitor is shown connected to an oxide-resistant terminalpin 142 gnd. The oxide-resistant terminal pin 142 gnd is attached to theferrule 134 either by a gold braze 165 or a laser weld 157 (not shown),as previously disclosed. It is understood by those skilled in the artthat the electrical connection on the right-hand side can alternatelycomprise an electrical connection material 152 connected to an ECAstripe or to the gold braze 154 a of the hermetic feedthrough for anessentially oxide-free electrical attachment.

FIG. 64C further shows a method of grounding a filter circuit board,wherein the filter circuit board has at least one internal (oralternatively external) ground plate 161. The ground plate 161 of thefilter circuit board is connected to an AIMD system ground, which inFIG. 64C is the ferrule 134 (terminal 3) of a hermetic feedthrough 132(not labelled). In this exemplary embodiment, illustrated on theleft-hand side is a ground pin 142 gnd, which is gold brazed 165 (oralternatively laser welded 157, not shown) into the ferrule 134 of thehermetic feedthrough. The terminal pin 142 gnd is shown attached in ablind via of the ferrule 134. An alternative embodiment is shown on theright-hand size, wherein the terminal pin 142 gnd′ extends through a viain the ferrule 134 to a body fluid side and a device side. The terminalpin 142 gnd, 142 gnd′ of FIG. 6C comprises an oxide-resistant material(or may alternatively comprise an oxide-resistant outer layer, such asan oxide-resistant coating, plating, or cladding) such that a very lowimpedance electrical connection can be made both to the terminal pin andto various via hole connections to the at least one filter circuit boardground plate 161. Filter circuit board ground plate 161 is shownconnected to six (or can alternatively be connected to “n” number)flat-through capacitor grounds (exemplary ground circuit traces 182 a,182 b are shown in FIG. 64B). Referring to FIG. 64B, one will appreciatethat the ground circuit traces 182 a, 182 b can be circuit board viaholes or include circuit traces. What is important is that both theground circuit traces 182 a and 182 b are conductively coupled throughthe circuit board via holes to the at least one ground plate 161. Thiscreates a multipoint grounding system, which makes flat-throughcapacitors very effective three-terminal filters for use in AIMDs,including filter circuit boards connected to a hermetic feedthrough ofan AIMD that effectively filters EMI.

FIG. 65C is another type of quad polar flat-through capacitor 210″intwhich is an internally grounded flat-through capacitor. Internallygrounded capacitors are more thoroughly described in U.S. Pat. No.5,905,627, the content of which is fully incorporated herein by thisreference. Referring to the internally grounded flat-through capacitorof FIG. 65C, the ground electrode plates 146 do not extend to the edgesof the flat-through capacitor 210″, but instead connect, as shown inFIG. 65D, to either two ground capacitor metallization areas 166 (notshown) or to a continuous ground capacitor metallization stripe 166 asshown in FIG. 65C.

FIG. 65D is a sectional view taken from section 65D-65D of FIG. 65Cillustrating the active electrode plates 144 a through 144 d and theground electrode plates 146 of the flat-through capacitor of FIG. 65C.

FIG. 65E shows the top view of a device side internally groundedflat-through capacitor 210″int FIGS. 65C and 65D edge-mounted in atombstone position. As illustrated, the flat-through capacitor 210″intat least partially shields the open windows of the insulator 156. Theterm “open windows” refers to an area that is not shielded such thatdangerous EMI fields can enter and radiate through. The internallygrounded flat-through capacitor 210″ mounted to a hermetic feedthroughas shown in FIG. 65E works similarly to the door of a microwavecomprising a metal plate perforated with holes. As microwave ovens, forconvenience, have a glass window so one can watch the food being cooked,the holes of the metal plate encased by the glass window comprises acalculated hole diameter such that the perforated metal plate becomes awave guide having wave beyond cutoffs so that dangerous microwave energyused to cook the food cannot get through the holes of the metal plate.Just as the perforated metal plate of the microwave door effectivelyshields at least a portion of the microwaves from escaping from the ovento the outside where one is watching the food cook, so too does theinternally grounded flat-through capacitor 210″int and its associatedground electrode plates effectively shield at least a portion of theopen windows of the insulator 156 of the hermetic feedthrough fromletting undesirable EMI into the device side (inside) of the housing ofan AIMD. As such, it is therefore not necessary that the open windows ofthe insulator 156 be completely shielded, as evidenced by everydaymicrowave ovens. Accordingly, the design of FIG. 65E carefully accountsfor the width of the insulators 156 and the width of the flat-throughcapacitor 210″int, such that, any EMI that can undesirably couple,cannot pass through. In other words, the internally groundedflat-through capacitor provides sufficient shielding of the hermeticfeedthrough such that the open window portions act as effective waveguides having beyond cutoffs to prevent dangerous EMI entry into thedevice side of an AIMD.

FIG. 65F is a cross-sectional view taken from section 65F-65F of FIG.65E. One can see that the flat-through capacitor 210″int is no longerconnected directly to the ferrule 134 as shown in FIG. 65B. Instead, atthe center, the capacitor ground electrode plates 146 are connected tothe ground capacitor metallization 166′. There is an electricalconnection material 151 that connects between the ground capacitormetallization 166′ and a peninsula 139 or bridge 141 of the ferrule 134.Peninsulas and bridges are more thoroughly disclosed in U.S. Pat. No.6,765,780, the content of which is fully incorporated herein by thisreference. On the device side, nail-head leadwires 142 a′ through 142 d′are shown. It is appreciated that the previously described round wires,flat ribbons, or other types of connections can alternatively be used.

FIG. 65G illustrates a hybrid flat-through capacitor 210″hyb. Thishybrid design comprises edge ground capacitor metallizations 166 and acenter ground capacitor metallization 166′ as shown.

FIG. 65H is a sectional view taken from section 65H-65H of FIG. 65Gillustrating the active electrode plates 144 a through 144 d and theground electrode plates 146 of the flat-through capacitor of FIG. 65G.Referring now to FIG. 65H, the quad polar active electrode plates 144 athrough 144 d each respectively connect to an active capacitormetallization 164 a through 164 d of the flat-through capacitor 210″hyb,as indicated. The flat-through capacitor 210″hyb also comprises groundcapacitor metallizations, the ground capacitor metallizations comprisingan edge ground capacitor metallization 166 on the left-hand side and theright-hand side of the flat-through capacitor and a ground capacitormetallization 166′ positioned in the center of the flat-throughcapacitor. The ground electrode plates 146 are electrically connectedexternally to the edge ground capacitor metallizations 166 on theleft-hand and right-hand sides of the flat-through capacitor andinternally to the center ground capacitor metallization 166′ therebyforming the hybrid filter flat-through capacitor 210″hyb. It is notedthat there can be a multiplicity of internal ground capacitormetallizations 166′, which can be particularly important for longerflat-through capacitors, as increasing the number of internal groundmetallizations in a substantially longer flat-through capacitor acts tokeep the inductance of the longer flat-through capacitor low.

FIG. 65I illustrates a hybrid filter flat-through capacitor 210″hybedge-mounted in a tombstone position to a device side of a hermeticfeedthrough 132 (not labelled). One can see that there are nail headterminal pins 142 a′ through 142 d′ that are connectable to AIMDelectronics, such as an AIMD active electronic circuit board (notshown). The hybrid filter flat-through capacitor 210″hyb is showngrounded at the right-hand side to an oxide-resistant area 248, 250using electrical connection material 152. It is understood that theoxide-resistant area 248, 250 may comprise a pocket, a pad (for example,a gold pocket or a gold pad), a metal addition or an ECA stripe. Anelectrical connection can also alternatively comprise a directconnection to at least a portion of gold braze 154 a. At the left-handside, shown is a ground electrical connection electrically connecting anend ground capacitor metallization 166 to a ground terminal pin 142gndusing electrical connection material 152. The ground terminal pin 142gndat the left-hand side is shown gold brazed or welded to the ferrule 134of the hermetic feedthrough 132. At the center of the hybrid filterflat-through capacitor 210″hyb, an internal ground connection to anoxide-resistant area 248, 250 is also shown. The ferrule 134 of thehermetic feedthrough of FIG. 65I comprises either a peninsula 139 or abridge 141, the peninsula or the bridge being integrally formed as acontinuous part of the ferrule 134. As defined herein, a peninsula 139partially extends inwardly into a ferrule opening 131 and a bridge 141extends completely across a ferrule opening 131 (not labelled). A deviceside ground terminal pin 142gnd extends through a capacitor conductivepassageway (a capacitor via hole) of the capacitor dielectric body 148(not labeled). The ground terminal pin 142gnd is conductively andmechanically connectable to one of the peninsula 131 and the bridge 141of the ferrule 134 of the hermetic feedthrough. As previously disclosed,the hybrid filter flat-through capacitor 210″hyb may comprise either asingle internal ground connection or alternatively multiple internalground connections. It is desirable that the hybrid filter flat-throughcapacitor 210″hyb have a multiplicity of ground plates, the multiplicityof ground plates being oriented in a tombstone position such that thehybrid filter flat-through capacitor 210″hyb at least partially shieldsradiated EMI from penetrating directly through any open windows of theinsulator 156 of the hermetic feedthrough. It is appreciated that theinsulator 156 can be a single insulator or comprise two or more separateinsulators, such as shown in FIG. 65I. Again, it is important that thedesign qualification of a filtered feedthrough 122, such as illustratedin FIG. 65I, include wave guide calculations and suitable filterperformance testing, including insertion loss at high frequency toassure EMI is effectively attenuated. It is also extremely importantthat, for all new EMI filter capacitor designs, filter capacitorinsertion loss and attenuation be measured at various frequencies.Ideally, these measurements should be swept measurements using a networkor spectrum analyzer. A critical capacitor EMI filter performance metricis its insertion loss, which is measured in decibels (dB). Measurementsof capacitance, ESR, insulation resistance and dielectric withstandingvoltage are other valuable capacitor measurements, however, thesemeasurements do not directly measure the RF performance of a filtercapacitor. As such, it is critical that the insertion losscharacteristics of every new EMI filter capacitor design be thoroughlyevaluated at least as a part of the initial qualification of the productand the insertion loss specified to ensure EMI attenuation iseffectively achieved, thereby preventing undesirable and potentiallyAIMD therapy delivery malfunctions from occurring.

FIG. 65J is a cross-sectional view taken from section 65J-65J of FIG.65I showing a filtered feedthrough 122 comprising the hybrid filterinternally grounded flat-through capacitor 210″hyb attached to ahermetic feedthrough 132 (not labelled). Illustrated is quad polarhybrid filter flat-through capacitor 210″hyb comprising an internalground connection at its center 166′ and edge ground connections at itstwo end ground capacitor metallizations 166. Such a hybrid filter groundconnection is important if the flat-through capacitor gets very long, asit is not desirable that the active electrode plates be located distantfrom the system ground. The hybrid ground connection of the presentapplication is also known as a multipoint grounding system, whichguarantees highly effective EMI filter performance at high frequencies.Another way of looking at this is that multipoint grounding does notallow too much inductance to build up across the critical groundelectrode plates 146.

As previously described, the edge ground capacitor metallizations 166 ofthe hybrid filter flat-through capacitor 210″hyb can be connectable toan oxide-resistance area 248, 250, such as a pocket, a pad, a conductivestripe, or even a hermetic braze of the hermetic feedthrough, which isshown on the right-hand side of FIG. 65J. The oxide-resistant area ofFOG. 65J is attached to the ferrule 134 of the hermetic feedthrough ofthe filtered feedthrough 122. The oxide-resistant area 248, 250 maycomprise a gold pocket, a gold pad, a noble metal addition, for example,a metal addition comprising platinum, gold, palladium, or alloysthereof, an ECA stripe attached to a noble metal area of a ferrule, suchas a noble metal laminated foil, a metallization, a vapor depositedfilm, a plating, or a coating, or combinations thereof. An electricalconnection material 152 is used to make such electrical connections tothe oxide-resistance area 248, 250. It is understood by those skilled inthe art that an oxide-resistant attachment can also be made to the goldbraze 154 a of the hermetic feedthrough.

On the left-hand side of the hybrid filter flat-through capacitor210″hyb of FIG. 64J is an oxide resistant ground terminal pin 142gnd.The oxide-resistant ground terminal pin 142gnd may be attached to theferrule 134 of the hermetic feedthrough 132 (not labelled) by either agold braze or a laser weld; however, other joining methods can be usedto attach the oxide-resistant ground terminal pin 142gnd, includingmicro-welding, micro-TIG welding, ultrasonic welding, resistancewelding, friction welding, butt welding, arc welding, gas welding,projection welding, flash welding, upset welding, solid state welding,diffusion welding, induction welding, percussion welding, electron beamwelding, multi-stage brazing, or reactive brazing. While theoxide-resistant ground terminal pin 142gnd on the left-hand side of FIG.64J is shown attached in a blind via of the ferrule 134, alternatively,the oxide-resistant ground terminal pin 142gnd can pass all the waythrough a via hole of the ferrule 134 of the hermetic feedthrough aspreviously disclosed in FIG. 64C. It will also be understood by thoseskilled in the art that an insulator washer 162 typically residesbetween the hybrid filter flat-through capacitor 210″hyb and theinsulator 156 of the hermetic feedthrough. It will also be understoodthat the insulator washer 162 will also similarly reside in all of thefiltered feedthroughs 122 of the present application having filtercapacitors attached to the insulator 156 of the hermetic feedthrough. Itis noted that, for simplicity, the insulator washer of the figures ofthe present application is not cross-hatched.

FIG. 65Ja is generally taken from section 65Ja-65Ja of FIG. 65Jillustrating an embodiment comprising a ground terminal pin 142gndpassing all the way through the ferrule 134 of a hermetic feedthrough.The ground terminal pin 142gnd can be electrically and hermeticallyattached to the ferrule 134 by a gold braze 165 or a laser weld 157 orany of the joining methods previously disclosed.

FIG. 65Jb is generally taken from section 65Jb-65Jb of FIG. 65Jillustrating an embodiment of an oxide-resistant area 248, 250 having ametallization layer 225 overlaid by an electrically conductive adhesive(for example an ECA stripe or an ECS dot) 223. ECA stripes overmetallization layers are more thoroughly described in U.S. provisional62/979,600, the content of which is fully incorporated herein by thisreference. In the embodiment of FIG. 65Jb, the electrical connectionmaterial 152 contacts at least a portion of the ECA stripe 223. Theelectrical connection material 152 is also shown contacting a portion ofthe ferrule 134, however, the connection to the ferrule is not requiredas the ferrule 134, if made of an easily oxidizable material, such astitanium, can heavily oxidize as previously disclosed.

Further regarding titanium, it is generally understood that: 1) titaniumhas a great chemical affinity for combining with oxygen; and 2) titaniumdoes not have a great affinity for combining with any other chemicals.It is generally understood that, in open air, freshly machined orcleaned titanium quickly forms a layer of oxides. This formation ofoxides creates a natural passivity that inhibits reactions with otherchemicals, such as salt or oxidizing acid solutions. The result is thattitanium has superior corrosion resistance. However, titanium oxidelayers can be present on a titanium ferrule at the time an electricalconnection material is applied. Even if titanium oxide layers areremoved prior to applying electrical connection material, the titaniumcan re-oxidize later on. For example, during laser welding of theferrule 134 to the AIMD housing 124, substantial localized heat may begenerated, which can accelerate titanium oxide layer formation. Theindustry generally believes that titanium oxide layers will not form ontitanium components internal the AIMD housing once hermetically sealed,mostly because AIMDs can be assembled in or back-filled with an inertgas, such as helium, nitrogen or argon. The industry typically does sowith the intent of inhibiting oxidation of sensitive metals liketitanium. This belief is erroneous. Materials of construction used inthe manufacture of AIMDs, such as polymers, plastics, adhesives,elastomers and the like, and even the printed circuit boards (PCBs)themselves inside the AIMD housing, generally have some level of gasestrapped within their structures, for example, moisture, oxygen, otheroxygen-containing gases, or even undetected residues comprising same,that eventually outgas during the operating life of the AIMD.Furthermore, processes that can involve increased temperature likewelding, curing or heat treatment processes, or even actions havingtemperature shifts, such as are possible during shipping, can acceleratesuch outgassing. Hence, even if an AIMD is manufactured in an inert gasenvironment, or backfilled with an inert gas, such ‘heating’ of certainmaterials of construction can release oxygen, oxygen-containing gases orwater vapor into an otherwise hermetically sealed environment causingthe formation of oxide layers on easily oxidizable materials liketitanium. The formation of such an oxide layer increases the RF groundimpedance, which seriously degrades EMI filter performance. Moreover,even when titanium is heated during welding, titanium oxides form evenfaster, and as the temperature reaches titanium's melting point (1,668°C., 3034° F.), the oxides typically dissolve into solution and cancontaminate the weld pool, which can cause an impure and/or a weak weld.This is why special care is generally taken to minimize exposure oftitanium components to oxygen during welding, such as employing a shieldgas, for example, argon or helium, or welding in a full vacuum (as isthe case with electron beam welding). Regardless, welding, even laserwelding as typically used by AIMD manufacturers, can cause heating alongthe weld seam of the AIMD, which may also involve heating of the deviceside ferrule surface as well. Hence, it is conceivable that when exposedto such heating by laser welding, the titanium ferrule 134, and inparticular the device side ferrule surface, can undesirably re-oxidize.The inventors studied the effect of titanium oxides on feedthroughfilters, measuring ESR/insertion loss (IL) pre- and post-laser welding.The inventors observed that post-laser welding, the ESR measurements ofsome feedthrough filters of a very large lot increased from thepre-laser welding measurement by orders of magnitude. To this day, whenattachment is made directly to titanium or other oxidizable metalwithout the presence of an oxide-resistant intermediary between thetitanium and the electrical attachment material, the inventors havefound that, while most parts in a production lot remain within ESR/ILspecification post-laser welding, there consistently are some parts inthis same lot that fail ESR/IL horribly. Thus, since failing ESRmeasurements remain unpredictable even under protective laser weldingprotocols, attaching to an ECA stripe without an oxide-resistantintermediary is a highly undesirable practice. Accordingly, thegenerally accepted belief that a titanium oxide layer will not form ontitanium components internal an AIMD housing once hermetically sealedsimply because AIMDs can be assembled in or back-filled with an inertgas is flawed and inaccurate. Thus, electrically connecting to an easilyoxidizable material such as titanium, more particularly, the depositionof an ECA stripe, without an intermediary oxide-resistant area 248, 250is highly undesirable, as such electrical connections have proven to bea highly unreliable due to re-oxidation and related increasingresistance. For more detail referring to the effects of oxide layerformation on EMI filtering, refer to the paper entitled, “DissipationFactor Testing is Inadequate for Medical Implant EMI Filters and OtherHigh Frequency MLC Capacitor Applications”, ISSN: 0887-7491, presentedat CARTS 2003: 23rd Capacitor and Resistor Technology Symposium, Mar.31-Apr. 3, 2003, the content of which is fully incorporated herein bythis reference.

FIG. 65Jc is taken from section 65Jc-65Jc of FIG. 65J. In thisembodiment, a metal addition 159 is shown welded 229 to the ferrule 134.There are various methods of attaching metal additions to the ferrule,which are more thoroughly disclosed in U.S. Pat. No. 9,931,514, thecontent of which is fully incorporated herein by this reference. Theelectrical connection material 152 must contact at least a portion ofthe metal addition 227 as shown to form a reliable oxide-resistantelectrical connection.

FIG. 65Jd is very similar to FIGS. 65Ja through 65Jc, except that inthis embodiment, the electrical connection material 152 at leastpartially contacts a gold braze 154 a. Electrical connection to the goldbraze of a hermetic feedthrough is disclosed in U.S. Pat. No. 6,765,779,the content of which is fully incorporated herein by this reference.

Referring once again to FIGS. 65J, 65Ja through FIG. 65Jd, it isappreciated that any of the filter capacitors of the present applicationcan be grounded in a like manner.

FIG. 65K is very similar to FIG. 65I illustrating a top view of anembodiment of a hybrid filter flat-through capacitor 210″hyb mounted ina tombstone position, except that instead of the bridge 141 of theferrule 134 of the hermetic feedthrough, a peninsula 139 is shown. Aspreviously disclosed, the hybrid filter flat-through capacitor 210″hybat least partially effectively blocks direct penetration of EMI throughthe insulator 156 of the hermetic feedthrough. Additionally, theinsulator 156 of FIG. 65I not a single insulator as is the insulator 156of FIG. 56K. The insulator 156 of FIG. 65K is modified to accommodatethe peninsula 139. The hybrid filter flat-through capacitor 210″hyb is athree-terminal capacitor, as are hybrid feedthrough filter capacitors.Hybrid feedthrough filter capacitors are disclosed in U.S. Pat. No.6,765,780, the content of which is fully incorporated herein by thisreference. As previously disclosed, the ferrule 134 of the hermeticfeedthrough of the filtered feedthrough 122 can comprise “n” number ofpeninsulas 139 so that a multipoint grounding system can be created.Referring to FIG. 65K, similar to the hybrid feedthrough filtercapacitor of the '780 patent, grounding of the hybrid filterflat-through capacitor 210″hyb comprises electrical connections of atleast one edge ground capacitor metallization 166 and at least oneinternal ground capacitor metallization 166′ (or internal groundconnection). Shortening the bridge, as taught by the '780 patent, is asimple variation of just shortening up the bridge to make said bridge apeninsula. An advantage of shortening up the bridge to make a peninsulais that the hermetic feedthrough requires only one insulator 156, whichcan be gold brazed 154 a in a single operation to the ferrule 134 of thehermetic feedthrough.

Referring once again to FIG. 65K, electrically connecting the activecapacitor metallization 164 a through 164 d and 164′a through 164′d tothe respective terminal pins 142 a through 142 d and 142′a through 142′dis best illustrated in FIG. 65L and FIG. 65M. FIG. 65L is a side view65L-65L of FIG. 65K illustrating the active capacitor metallizations 164a through 164 d and 164′a through 164′d connected with respectiveterminal pins 142 a through 142 d and 142′a through 142′d using anelectrical connection material 145. The active capacitor metallizationsof the hybrid filter flat-through capacitor 210″hyb partially extendalong the surface of the side of the filter capacitor as shown, in orderto secure the terminal pins to the filter capacitor in a mechanicallyand electrically robust manner. In other words, attachment of theterminal pins to the extended active capacitor metallization increasesthe bonding area of the electrical connections providing secureattachment that sustains mechanical shock and vibration. Referring onceagain to FIG. 65L, it is appreciated that the active capacitormetallizations 164 a through 164 d and 164′a through 164′d must wrapover the edge of the thickness of the hybrid filter flat-throughcapacitor 210″hyb, which is shown at the top and the bottom of thetombstone mounted capacitor so that electrical connection of the activeelectrode plates of said hybrid filter capacitor are made. Alsoillustrated in FIG. 65L are edge ground capacitor metallizations 166 andat least one internal ground capacitor metallization 166′ (shown in thecenter of the hybrid filter capacitor). The internal ground capacitormetallization 166′ must also wrap over the edge of the thickness of thehybrid filter flat-through capacitor 210″hyb at the top and the bottomof the tombstone mounted capacitor for proper connection to the hybridfilter capacitor's ground electrode plates 146. An electrical connectionmaterial 152 connects the hybrid filter capacitor edge ground capacitormetallization 166 on the right-hand side to the ferrule surface 133 andto an oxide-resistant ground terminal pin 142gnd on the left-hand side.Electrical connection to the ferrule surface 133 on the right-hand sidecan be made using any one of the oxide-resistant area 148, 150embodiments of FIGS. 65J, 65Ja through 65Jd. Electrical connection canalternatively be made by a direct connection to a gold braze 154 a.

FIG. 65M is the opposite (reverse) side view taken from section 65M-65Mof FIG. 65K. In this view, one can see the centered internal groundterminal pin 142gnd. The ground terminal pin 12gnd is conductively andmechanically connected to at least one of a peninsula 139 or a bridge141 of the ferrule 134 of the hermetic feedthrough. The centeredinternal ground terminal pin 142gnd is either gold brazed or welded tothe peninsula 139 or to the bridge 141 of a ferrule structure 134.Importantly, the ground terminal pin 142gnd provides a very lowresistance and low impedance electrical connection to the hybridflat-through capacitor grounding system 210″hyb so that high frequencyRF energy can be diverted to the ferrule and then, in turn, to the AIMDhousing (not shown). It is appreciated that all the ferrule structuresdescribed herein are configured to be laser welded into an opening ofthe housing of an AIMD.

FIG. 65N is a top view of an embodiment of a hermetic feedthrough 132.Shown are six active terminal pins 142 a through 142 f, whichalternatively may be co-sintered paste-filled vias. As illustrated, theactive terminal pins 142 a through 142 f pass through the insulator 156of the hermetic feedthrough 132 in non-conductive relationship with theferrule 134. On the left-hand side of FIG. 65N, an oxide-resistant area248 is shown, which in FIG. 65N may be a circular gold pocket-pad. It isunderstood that the gold pocket-pad may be any shape, including acircle, a rectangle, a square, an oval, a custom designed shape, or anyshape commensurate with the needs of an application. Alternatively, thegold pocket-pad can instead be an ECA stripe as previously disclosed. AnECA stripe overlays an oxide-resistant metallized area as disclosed inU.S. provisional 62/979,600. On the right-hand side of FIG. 65N, shownis a ground terminal pin 142gnd. The ground terminal pin 142gnd iseither gold brazed 165 or welded 229 directly to the ferrule 134 andcomprises an oxide-resistant material such as previously disclosed. Boththe right-hand and left-hand sides of the insulator 156 are curved, butcan alternatively be a rectangular shape, which simply means that theground locations are moved further out. In other words, the shape of theinsulator can take on any shape that is required for an application.Referring once again to FIG. 65N, illustrated is what is known as a dualinline staggered pin feedthrough terminal pin layout.

FIG. 65O is an isometric view of a dual inline hybrid filterflat-through capacitor 210″hyb. One can see on the far left-hand side ofthe hybrid filter flat-through capacitor 210″hyb that there is a firstground capacitor metallization 166 on the very top of the dielectricbody 148 of said filter capacitor, while on the right-hand side of thehybrid filter flat-through capacitor 210″hyb there is a second groundcapacitor metallization 166 at the very end of the dielectric body 148of said filter capacitor. Visible are also six active capacitormetallizations 164 a′ through 164 f on the top surface of the dielectricbody 148 of the hybrid filter flat-through capacitor 210″hyb. There arealso six corresponding active capacitor metallizations 164 a through 164f on the bottom side of the dielectric body 148 of the hybrid filterflat-through capacitor 210″hyb that are not visible.

FIG. 65P is an isometric view of the hybrid filter flat-throughcapacitor 210″hyb of FIG. 65O illustrating the active electrode plates144 a through 144 f and the ground plates 146 residing within thedielectric body 148 of said filter capacitor. In the embodiment shown,each active electrode plate 144 a through 144 f is sandwiched between apair of ground electrode plates 146. Each active electrode plate 144 athrough 144 f is electrically connected to its respective activecapacitor metallization 164 a′ through 164 f′. Each ground electrodeplate 146 is electrically connected to the left-hand side and theright-hand side ground capacitor metallizations 166. It is noted that,while the first ground capacitor metallization 166 on the left-hand sideis disposed on the top of the hybrid filter flat-through capacitor210″hyb and the second ground capacitor metallization 166 on theright-hand is disposed on the end of said filter capacitor, the groundcapacitor metallizations 166 can be positioned reversely, meaning theleft-hand side can be an end ground capacitor metallization and theright-hand side can be a top ground capacitor metallization. Likewise,both ground capacitor metallizations can be top ground capacitormetallizations or, alternatively, both can be end ground capacitormetallizations. It is also understood that although just one activeelectrode plate is shown for connection to a feedthrough leadwire, inpractice, multiple “n” number of active electrode plates and groundelectrode plates can be electrically connected to each feedthroughleadwire.

FIG. 65Q is a top view of the dual inline hybrid filter flat-throughcapacitor 210″hyb of FIGS. 65O and 65P mounted on a hermetic feedthrough132 (not labelled). The capacitor shown has a ground connection at theleft-hand side and the right-hand side of the ferrule 134 of thehermetic feedthrough. The ground connections are better understood inthe cross-section of FIG. 65R. As can be seen in FIG. 65Q, there are sixactive capacitor metallizations 164 a′ through 164 f′ (not labelled),hence the hybrid filter flat-through capacitor 210″hyb is a hex-polarthree-terminal hybrid filter capacitor. Also shown in this top view arethe active terminal pins 142 a′ through 142 f. Terminal pins 142 a′through 142 d′ are nail head terminal pins, the nail head being suitablefor attachment to the active capacitor metallizations 164 a′ through 164d′ (not labelled) of the hybrid filter flat-through capacitor 210″hybusing an electrical connection material 151. Terminal pins 142 e′ and142 f′ are lying sideways on their respective active capacitormetallizations 164 e′ and 164 f′ (not labelled) and are attached to saidmetallizations using an electrical connection material 145. It isappreciated that these terminal pins can be round wires, flat ribbon,wire bonding cables, leadwires, lead wires, pins, lead conductors orsimilar as previously disclosed. Alternatively, the electricalconnection to the active capacitor metallizations can even be made to anAIMD active electronic circuit board butted up directly to and matingwith said active capacitor metallizations without the need for aleadwire interconnection. The dual inline hybrid filter flat-throughcapacitor 210″hyb of FIG. 65Q is wide and completely covers the entiresurface of the insulator 156 of the hermetic feedthrough. As such,waveguide calculations are unnecessary because the ground electrodeplates of the hybrid filter flat-through capacitor 210″hyb completelyshield any open windows mitigating any threat of direct penetration byelectromagnetic interference radiation through the insulator 156.

FIG. 65R is a cross-sectional view taken from 65R-65R of FIG. 65Q. Shownis the active electrode plate 144 a associated with the terminal pin 142a′. It is appreciated that in practice multiple active electrode plates(“n” number of active electrode plates 144) are interleaved with groundelectrode plates 146 sandwich style.

FIG. 65S is taken from 65S-65S of FIG. 65Q. Shown is one of themultiplicity of interleaved ground electrode plates 146. A variety ofgrounding methods for the ground electrode plate 146 and associatedground capacitor metallizations 166 are shown. On the left-hand side, anoxide-resistant area 248, 250 (such as a gold pocket or a gold pad) isused to provide electrical connection to the ferrule 134 of the hermeticfeedthrough. On the right-hand side, a ground terminal pin 142gnd thatis either gold brazed 165 or welded 229 to the ferrule 134 is used toprovide electrical connection to the ferrule 134 of the hermeticfeedthrough. Alternatively, an electrical connection material may beused on the right-hand and the left-hand sides to contact a gold braze154 a to achieve the oxide-resistant electrical connection. Referringonce again to FIG. 65S, one can see that active terminal pins 142 b′ and142 d′ comprise nail-head structures, which can be attached by BGA 151or similar mounting methods to the active capacitor metallizations 164(not labelled). Active terminal pins 142 e′ are longitudinally alignedin parallel with the surface of the active capacitor metallizationsusing electrical connection material 145 as shown. Such parallelalignment is desirable for a higher surface area attachment, which isgenerally more resistant to shock and vibration loads. Terminal pin 142e′ illustrates a round wire and terminal pin 142 f′ illustrates a flatribbon, both of which can be attached to the active capacitormetallization by an electrical attachment material 145 as shown or,alternately, by other industry methods such as wire bonding orultrasonic bonding.

FIG. 65T is taken from 65T-65T of FIG. 65Q. Illustrated is an activeelectrode plate 144 b that is associated with terminal pin 142 b′. It isunderstood that all of the figures illustrating filtered feedthrough 122typically comprise an insulation washer 162 disposed between theflat-through capacitor 210″hyb and the device sides of the insulator 156and the ferrule 134 as illustrated in the exemplary embodiments of FIG.65T. The insulating washer 162 provides a mechanical attachment to atleast one of the ferrule 134 and the insulator 156, while, at the sametime, said insulating washer insulates the terminal pins one from theother; for example, the insulating washer 162 insulates between twoactive terminal pins and also insulates between an active terminal pinand a ground connection, such as between an active terminal pin and aground terminal pin. The insulation washer 162 is important because itprevents high voltage flashover, such as is possible in an implantabledefibrillator application, and also inhibits undesirable migration ofmaterials, which can lead to reduced insulation resistance betweenadjacent circuits (channels) or any of the active circuits and ground.It is noted that, for simplicity, the insulator washer 162 of thefigures of the present application is not cross-hatched.

FIG. 66 illustrates a bipolar X2Y attenuator 210″, bipolar meaning thatthe X2Y attenuator 210′″ can filter two leadwires at the same time. Thisis better understood by examining the internal active electrode plates144 a and 144 b of FIG. 67. The active electrode plates 144 a areconnected to the left-hand side active capacitor metallization 164 a.The right-hand side active electrode plates 144 b are connected to theright-hand side active capacitor metallization 164 b. The activeelectrode plates are interleaved with the ground electrode plates 146 ofFIG. 68. This interleaved configuration is illustrated in FIG. 69,showing that active electrode plates 164 a and 164 b are bothinterleaved with a plurality of ground electrode plates 146. It isappreciated that any number of active and ground electrode plates can beinterleaved to create a desired line-to-line or a line-to-ground amountof capacitance or filtering. For example, if one wanted a great deal ofline-to-line filtering, that is, filtering between active capacitormetallizations 164 a and 164 b, then one eliminates the interleavedground electrode plate 146, which thus increases the effectivecapacitance area (ECA) between these two opposed active electrodeplates. However, if one wanted mostly line-to-ground filtering, in otherwords, filtering from active capacitor metallization 164 a to groundcapacitor metallization 166 and active capacitor metallization 164 b toground capacitor metallization 166, then one interleaves groundelectrode plates 146 as illustrated in FIG. 69.

FIG. 69B is similar to FIG. 66 except that instead of the discontinuousdiscrete ground capacitor metallizations 166 a and 166 b of FIG. 66, acontinuous ground capacitor metallization 166 is illustrated. Thecontinuous ground capacitor metallization 166 of the X2Y attenuator210′″ is a metallization band disposed all the way around said X2Yattenuator. Either of the ground capacitor metallization embodiments ofFIGS. 66 and 69B can be used for the X2Y attenuator 210′″ as the groundelectrode plates 146 shown in both FIGS. 66 and 69 are configured toselectively extend to the edge of each long side of the dielectric bodyof the X2Y attenuators. The selective extension of the ground electrodeplates allows contact to be made to either ground capacitormetallization embodiment. The ground electrode plate edge extensions areillustrated in the discontinuous discrete ground capacitormetallizations 166 a and 166 b of FIGS. 68 and 69 and in the continuousground capacitor metallization 166 of FIG. 69C. In summary, theselective extensions of the ground electrode plates 146 at the edge ofthe long sides of the dielectric body of the X2Y attenuator contacts theground capacitor rnetallization(s) of said X2Y attenuator regardless ofwhether said ground capacitor metallization comprises a continuousground capacitor metallization band as illustrated in FIG. 69 ordiscontinuous discrete ground capacitor metallization bands asillustrated in FIG. 66.

FIG. 69C is a sectional view illustrating the active electrode plates144 a, 144 b and the ground electrode plate 146 that interleave the X2Yattenuator of FIG. 69B. The X2Y attenuator 210′″ looks similar inphysical appearance to the flat-through capacitors 210″ previouslydisclosed, however, the X2Y attenuators of FIGS. 66 and 69B are uniquebipolar devices that can filter two leadwires of the hermeticfeedthrough at the same time. Simultaneous filtering of two feedthroughleadwires is possible because the active electrode plates Ca and Cb ofthe X2Y attenuators FIGS. 66 and 69B are designed such that the X2Yattenuator essentially comprises two different capacitors, one capacitorcomprising the active electrode plates Ca electrically connected to anactive capacitor metallization 164 a and a second capacitor comprisingthe active electrode plates Cb electrically connected to an activecapacitor metallization 164 b. Each active electrode plate 164 a, 164 bis sandwiched by ground electrode plates 146, and are connected to theirrespective active capacitor metallizations 164 a and 164 b, thereby areelectrically connectable to two leadwires of a hermetic feedthrough forEMI filtering of said leadwires. As such, one leadwire of the hermeticfeedthrough is electrically connectable to the active electrodemetallization 164 a and a second leadwire of the hermetic feedthrough iselectrically connectable to the active electrode metallization 164 b.

FIG. 69D is the schematic diagram of the X2Y attenuator 210′″ of FIGS.66 and 69B. Shown is a line-to-line capacitance Ca-b between lines 142 aand 142 b. Also shown are line-to-ground capacitances Ca and Cb groundedto the ferrule 134, which are both system grounds. As previouslydescribed, by adjusting the size of the active and ground electrodeplates or by selectively limiting the number of ground electrode plates,the line-to-line capacitance Ca-b versus the amount of line-to-groundcapacitances Ca and Cb can be adjusted.

It is understood that X2Y attenuators come in various sizes and shapesand are not always bipolar devices. X2Y attenuators may have a number ofgeometries and a number of additional POLES. The X2Y attenuators of thepresent application are mounted to an EMI filter circuit board for usein an AND for the purpose of illustration; however, can also alternatelybe used is various other electronic circuitry as well. The X2Yattenuators 210′″ of FIGS. 66 and 69B are both bipolar X2Y attenuators.

FIG. 70A illustrates a filter circuit board 130 mounted at, near oradjacent the device side of an AIMD hermetic feedthrough 132 (notlabelled). The circuit board 130 of FIG. 70A is mounted to the deviceside of the ferrule 134 as shown. The filter circuit board 130 of thepresent application can be a printed circuit board, an FR4 board, amulti-layer board, an alumina board, a flexible circuit board, or anyother type of circuit board known in the art. As previously disclosedfor flat-through capacitors 210″, the circuit board 130 of FIG. 70A hasone or more ground plates 161, which can be internal ground plates,external ground plates, or a combination of internal and external groundplates. The ground plates are very important in providing low impedanceRF decoupling for each of the X2Y attenuators 210″. A primary differencebetween X2Y attenuators 210′″ and the flat-through capacitors 210″previously disclosed is that the circuit current of an AIMD does notpass through the active electrode plates of the flat-through capacitor.The only currents passing through the active electrode plates of theflat-through capacitor are the decoupled EMI currents.

FIG. 70B is taken from section 70B-70B of FIG. 70A, illustrating across-sectional view of the circuit board 130, including the at leastone circuit board ground electrode plate 161, which, in this case, isalso a shield electrode plate. Ground plates are very important forshielding or covering up at least the bulk of the insulator of ahermetic feedthrough. Emitters in close proximity to a patient having animplanted AIMD, such as cellular telephones, produce strong radiatedEMI, which can pass directly through the insulator of a hermeticfeedthrough to undesirably couple to sensitive AIMD electronic circuits.Filter circuit boards comprising ground electrode shield plates preventthat direct radiation of EMI energy. In the exemplary embodiment ofFIGS. 70A and 70B, the ground electrode plate 161 illustrated, which isalso the shield electrode plate, both reflects and absorbs incidentradiated energy. In order for the ground electrode plate 161 toeffectively reflect and absorb radiated EMI, the ground electrode platemust be connected to the system ground in a very low impedance manner,meaning that both the inductance and the resistance of the electricalconnection must be very low. It is appreciated that a multiplicity ofground electrode shield plates 161 can be used in the circuit board 130,including external ground electrode shield plates. Ideally, externalground electrode shield plates are disposed between the surface of thecircuit board facing the hermetic feedthrough and the top of theinsulator 156 of the hermetic feedthrough, as such a location mosteffectively reflects and absorbs radiated EMI impinging from the bodyfluid side of the AIMD.

Referring once again to FIG. 70B, illustrated is a radiated EMIimpinging the hermetic feedthrough from the body fluid side of the AIMD.The body fluid side, as illustrated in FIG. 70B, shows both conductedand radiated EMI. Radiated EMI is impinging directly against theinsulator 156 of the filtered feedthrough 122 attached to the AIMDhousing 124 (not shown). Importantly, the at least one circuit boardground plate 161, which is also a shield electrode plates, reflects andabsorbs this radiated EMI. There is also conducted EMI advancing fromthe body fluid side as illustrated. The conducted EMI is picked up bythe implanted leadwires (not shown) and conducted by antenna actionalong the leadwire of the hermetic feedthrough, which is thereby routedto the device side inside of the AIMD housing. Importantly, the X2Yattenuators 210′″ divert the EMI energy from each pair of leadwires towhich the X2Y attenuator is connected, for example, to terminal pins 142a and 142 b connected to their X2y attenuator respective activecapacitor metallizations 164 a and 164 b, to the common ground of theAIMD, which is the ferrule 134 and the AIMD housing 124 (not shown). Inthis way, the two different filter capacitors of the X2Y attenuatorsdesirably act as high frequency diverters.

Referring once again to FIG. 70B, illustrated are circuit board rivets213. Rivets 213 are well known in the art for connecting a ground viahole of the circuit board to the at least one ground plate 161, which inthis case is also a shield electrode plate. The rivet 213 can directlycontact an oxide-resistant area 248, 250 (not shown) or a gold braze 154c as shown. Alternatively, an electrically conductive material 155 (notshown) may provide electrical connection between said rivet 213 and theoxide-resistant area 248, 250, such as a gold pocket or gold pad, or thegold braze 154 c. Oxide-resistant areas including gold pockets, goldpads or equivalent oxide-resistant materials are more thoroughlydescribed in U.S. Pat. No. 10,350,421, the content of which is fullyincorporated herein by this reference. Alternative methods of groundingall types of filter circuit boards will be disclosed later. In allfilter circuit board cases, however, it is very important that anoxide-resistant ground connection be made to the ferrule 134 of thehermetic feedthrough of the AIMD.

Ground electrode plates, shield electrode plates, oxide-resistantgrounding methods and filter circuit boards are more thoroughlydescribed in U.S. Pat. No. 8,195,295, the content of which is fullyincorporated herein by this reference.

Referring back to the flat-through capacitors 210″ and the X2Yattenuators 210″ taught herein, it is noted that these capacitors are ofa low k dielectric (k<1,000), the dielectric constant being greater than0 and less than 1,000. These low k capacitors are the first filtercapacitors on the device side inside the AIMD housing, which divertundesirable and/or unwanted EMI to the ferrule and/or the AIMD housing.

FIG. 70C illustrates X2Y attenuators 210′″ in a tombstone mountingposition, consistent with the embodiments taught herein for theflat-through filter capacitor 210″. For example, the X2Y attenuator210′″ of FIG. 70A can have the active and ground electrode platesdisposed perpendicular to the ferrule and insulator device side surfacesof the hermetic feedthrough. The embodiment of FIG. 70C illustrateseight terminal pins 142 a through 142 h electrically connectedrespectively to the active capacitor metallizations 164 of the X2Yattenuators 210′″ using an electrical connection material 145.Additionally, the circuit board 130 of FIG. 70C is configured to exposethe gold braze 154 a between the insulator 156 and the ferrule 134 ofthe hermetic feedthrough. The ground capacitor metallizations 166 of theX2Y attenuators 210″ are directly connected to the gold braze 154 a ofthe hermetic feedthrough using an electrically conductive material 152.

FIG. 70D is an enlarged cross-sectional view taken from section 70D-70Dof FIG. 70C. Illustrated are the active electrode plates 144 g connectedto the left-hand side active capacitor metallization 164, the activeelectrode plates 144 h connected to the right-hand side active capacitormetallization 164 h, and the ground electrode plates 146 interleavedwith the active electrode plates, which are representative of theelectrode plate arrangement of the X2Y attenuators 210′″ of FIG. 70C.Additionally, FIG. 70D helps visualizing how the active and groundelectrode plates of the X2Y attenuator 210′″ are disposed in relation tothe ferrule 134 and the insulator 156 of a hermetic feedthrough when theX2Y attenuators are attached in a tombstone mounting position.

It is understood that the X2Y attenuator 210′″ can be grounded to theferrule 134 utilizing any of the methods previously taught herein,including but not limited to, oxide-resistant areas 248, 250, such asgold pockets, gold pads, or other oxide-resistant pockets and pads,peninsulas 139, bridges 141, grounding terminal pins 142gnd, ECA stripes223, 225 and metal additions 159, 229. Furthermore, the width of the X2Yattenuator 210′″ may be increased to accommodate a staggered leadwirehermetic feedthrough design. Wider X2Y attenuators 210′″ for staggeredleadwire hermetic feedthrough designs may be disposed at an angle totake advantage of the increased distance that exists between thestaggered leadwires. It is understood that the X2Y attenuators 210′″ canbe disposed in the tombstone position on top of circuit board 130, andthe circuit board 130 attached to the hermetic feedthrough asillustrated in FIGS. 70A and 70B.

FIG. 71A is taken from FIG. 25 of U.S. provisional 62/646,552 (the '552provisional), the content of which is fully incorporated herein by thisreference. FIG. 71A illustrates a hermetic feedthrough wherein theferrule 134 of said hermetic feedthrough comprises oxide-resistant areas248, 250, which are shown as gold pocket-pads.

FIG. 71B is taken from FIG. 27 of the '552 provisional showing a quadpolar rectangular feedthrough filter capacitor 210′ wherein the groundelectrode metallization 166 is electrically connected to theoxide-resistant areas 248, 250 (gold pocket-pads) using an electricallyconductive material 152.

FIG. 71C is taken from FIG. 31 of the '552 provisional illustrating afeedthrough filter capacitor 210′ attached to a hermetic feedthrough132, wherein a filter capacitor width 269 of the feedthrough filtercapacitor 210′ is greater than a ferrule width 267 of a ferrule 134 ofthe hermetic feedthrough 132. This embodiment is particularly enablingto the present invention as a k<1,000 or mid k filter capacitor (thedielectric material comprising a dielectric constant greater than 0 butless than 1,000) is less volumetrically efficient than the prior art1,200 k to 2,600 k dielectric filter capacitors, hence is typicallybigger than said prior art capacitors. In most AIMDs, such as cardiacpacemakers, ICDs, neurostimulators and the like, there is very littleheight available for the feedthrough filter capacitor 210′; however, itis generally possible to increase the filter capacitor width 269 of thefeedthrough filter capacitor 210′ if higher capacitance values areneeded. Accordingly, a k<1,000 filter capacitor, such as the feedthroughfilter capacitor 210′ of FIG. 71C, which comprises a dielectric constantgreater than 0 but less than 1,000 and a filter capacitor width 269greater than the ferrule width 267 of the ferrule 134 of a hermeticfeedthrough 132, is an enabling distinctive feature of the presentinvention. Furthermore, oxide-resistant areas 248, 250, in accordancewith the '552 provisional, provide a unique embodiment for attachingk<1,000 filter capacitors.

Referring once again to FIG. 71C, it is appreciated that, if highercapacitance is needed, feedthrough filter capacitors 210′ mayalternatively comprise a filter capacitor length 273 greater than alength of a ferrule opening 131 (not shown) of a hermetic feedthrough132. Given the importance of oxide-resistant attachment as previouslyexplained, that is, so that low inductance and low resistanceconnections of the ground capacitor metallization 166 of the feedthroughfilter capacitor 210′ to the ferrule 134 of the hermetic feedthrough 132can be made, and considering that a k<1,000 filter capacitor istypically larger in size than prior art filter capacitors in order tomatch prior art capacitance requirements, oxide-resistant areaattachment alternatives provide additional filtered feedthrough designoptions for meeting application filter requirements. For example,instead of a feedthrough filter capacitor 210′ comprising a short length273 such that the ground electrode metallization 166 can be attached tothe gold braze 154 a that hermetically seals the insulator 156 and theferrule 134 of the hermetic feedthrough 132, a feedthrough filtercapacitor 210′ can comprise a length 273 greater than a length of aferrule opening such that the ground electrode metallization 166 can beattached to oxide-resistant areas 248, 250 disposed on or within theferrule 134 of the hermetic feedthrough 132. Attachment of the groundelectrode metallization 166 is made using an electrically conductivematerial 152. Referring once again to FIG. 71C, it is understood thatthe feedthrough filter capacitor 210′ may comprise one of a width 269greater than the width of the ferrule 134 of the hermetic feedthrough132 (wherein the feedthrough filter capacitor overhangs at least oneedge or a flange of the ferrule), a length 273 greater than the lengthof a ferrule opening 131 (not shown) of the hermetic feedthrough 132, orboth a width greater than the width of the ferrule and a length longerthan the length of the ferrule opening of the hermetic feedthrough,wherein the ground electrode capacitor metallization 166 of thefeedthrough filter capacitor 210′ is attached to at least a portion ofan oxide-resistant area 248, 250 using an electrically conductivematerial 152. In summary, increasing the width 269 and/or the length 273of the filter capacitor significantly increases its volumetricefficiency.

Referring once again to FIG. 71C, one can see that the filter capacitorwidth 269 is defined by 269 e-269 e. Likewise, the filter capacitorlength 273 is defined by 273 e-273 e. Similarly, the ferrule width 267is defined by 267 e-267 e and the ferrule length 271 is defined by 271e-271 e.

FIG. 72A is similar to FIG. 71A except that the gold pocket-pads 248 arenow illustrated along the length of the ferrule 134. In this embodiment,the gold pocket-pads 248 are elongated and shaped to receive a length ofan oxide-resistant wire 250 as shown. The oxide-resistant wire 250 maybe selected from the group consisting of platinum, gold, tungsten,iridium, palladium, niobium, tantalum, ruthenium, rhodium, silver,osmium, and alloys or combinations thereof. The oxide-resistant materialof the ground terminal pins 182gnd may further be selected from thegroup consisting of platinum-based materials including platinum-rhodium,platinum-iridium, platinum-palladium, or platinum-gold and naturallyoccurring alloys such as platiniridium (platinum-iridium), iridiosmiumand osmiridium (iridium-osmium). The embodiment of FIG. 72A, may bedesigned for attachment of the oxide-resistant wire during a brazingoperation such that the oxide-resistant wire is attached at the sametime the feedthrough is hermetically sealed. For example, during asingle brazing operation, a first gold braze 154 a forms a hermetic sealbetween the insulator 156 and the ferrule 134, such as a titaniumferrule; a second gold braze 154 b forms a hermetic seal between each ofthe terminal pins/leadwires T and 142 and the insulator 156; and a goldbraze wire 250 disposed in the pocket-pads 248 melts and reflows withinthe pocket-pads 248. Instead of a gold braze wire 250, a third goldbraze (not shown) disposed within the pocket-pad 248 may alternativelybe used to attach an oxide-resistant wire 250 to the ferrule 134. Theuse of pocket-pads 248 allows wider and/or longer feedthrough filtercapacitors to be attached to a hermetic feedthrough, wherein a groundpath can be attached to an oxide-resistant material, and wherein theoxide-resistant material consists of a gold braze material 250 in theform of a gold braze wire or as a gold braze preform to attach anoxide-resistant wire.

It contemplated that a ribbon, a woven wire, a braided mesh, a braidedwire, a cable, pressed nano-particles, laminated nano-particles, pressedparticles, coils and the like can be used instead of the wire 250. Inaddition to gold or pure gold (99.99%), a gold alloy braze material mayalternately be used. A preferred gold alloy braze is one which containsmore than 50% gold by weight. Non-limiting examples include: 82Au-18In,88Au-12Ge, the various Johnson Matthey Pallabraze and Orobraze alloys,and the gold alloys of U.S. Pat. No. 4,938,922, the content of which isfully incorporated herein by this reference. Other acceptable metalsthat form a metallurgical bond to the underlying titanium ferrule,include platinum, palladium or any alloys thereof, including alloys ofgold. What is important is that the resulting pocket-pad isoxide-resistant, forms a metallurgical bond with the underlying basemetal of the ferrule (which is typically of titanium), and readilyaccepts an electrical connection. An electrical connection material,such as a solder, a thermal-setting conductive adhesive or a braze maybe used to form the electrical connection.

Referring once again to FIG. 72A, one can see that there are five activeterminal pins 142,136 and one telemetry pin marked T. It is appreciatedthat the telemetry pin T can optionally be hermetically sealed to aseparate insulator instead of in a single insulator 156 as shown.Additionally, any of the terminal pins 142,136 can be hermeticallysealed into two or more separate insulators 156. Each of the terminalpins 142,136 and the telemetry pin T can be hermetically sealed inindividual insulators. It is appreciated that the embodiment of FIG. 72Ais not meant to be limiting as any number of active and/or telemetrypins can be hermetically sealed to an insulator of a hermeticfeedthrough. Additionally, it is not necessary that the terminal pins bein-line as shown in FIG. 27 but can be hermetically in the insulator inany position required by an application. For example, the terminal pinsof a feedthrough can alternatively be hermetically sealed in one of astaggered terminal pin configuration, a dual in-line terminal pinconfiguration, diagonally spaced in pairs, or a custom terminal pinconfiguration.

Referring once again to FIG. 72A, the elongated pocket-pads 248 aregenerally very shallow and may be separately machined after the ferruleis made, or may alternatively be formed during the machining, stampingor metal injection molding of the ferrule 134. One convenient way tomanufacture the elongated pocket-pads 248 is with a ball-shaped cuttingtool of an end mill that only partially penetrates the surface of theferrule. The pocket-pads 248 are generally very narrow, for example, 1mil to 4 mils, allowing a small diameter oxide-resistant wire 250, forexample, less than 1 mil to 2 mils, to be used. As previously disclosed,oxides of titanium are generally only angstroms thick. Therefore, even a1 mil coating of an oxide-resistant material is sufficient to preventtitanium oxidation thereby providing an oxide-resistant attachmentsurface.

Referring now back to FIG. 71A, it is understood that the goldpocket-pads 248 of FIG. 71A can be elongated similar to the elongatedpocket-pads of FIG. 72A such that a thin gold wire can be used, therebyproviding a single elongated oxide-resistant attachment surface alongthe width at both ends of the ferrule 134. Referring again to FIG. 71A,it is also understood that the gold pocket-pads 248 can be made at thecorners of the ferrule 134 to facilitate suitable electrical connectionshould it be needed. Regardless of the oxide-resistant pocket-padlocation or configuration, the pocket-pad 248 design should be made sothat an oxide-resistant electrical connection can be made to the groundcapacitor metallization 166 of the filter capacitor, whether that groundcapacitor metallization 166 resides on the short side, the long side, orboth the short and the long sides of said filter capacitor.

FIG. 72B illustrates a filter capacitor 210′ mounted atop the hermeticfeedthrough of FIG. 72A forming a filtered feedthrough 122. Importantly,the telemetry pin T of the hermetic feedthrough is not included in thefilter capacitor 210′ because the telemetry signal is a high frequencysignal that is filtered by the filter capacitor 210′. In general, highfrequency filtering by a feedthrough filter capacitor 210′ cannot beapplied to telemetry pins, as the telemetry signal, being a highfrequency signal, is attenuated rendering the telemetry pin ineffective.All of the active terminal pins 142, however, passing through andelectrically connected to the filter capacitor 210′ are appropriatelyfiltered. Importantly, the ground capacitor metallization (termination)166, which contacts the filter capacitor's ground electrode plates 146,are electrically attached using an electrically conductive material 152such as a solder or a thermal-setting conductive adhesive. It is notedthat the electrically conductive material 152 of FIG. 72B is shownelectrically connecting across the full length of the oxide-resistantpocket-pad 248, 250, however, the electrically conductive material 152may alternatively at least partially contact the gold braze or wire 250associated with pocket-pad 248.

Referring once again to FIG. 72B, it is not necessary that theoxide-resistant pocket-pad 248, 250 extend the whole length of afeedthrough filter capacitor. It can extend, for example, for threequarters of the length and be centered and will work just fine from anelectrical high-frequency impedance point of view. The oxide-resistantpocket-pad 248, 250 can also be discontinuous, for example, two or threeshort oxide-resistant pocket-pad segments distributed along the lengthon each side of the ferrule 134 are sufficient in the event that thecost of the oxide-resistant material, such as a gold, is a concern.Since the oxide-resistant pocket-pad 248 of the present application islike a swimming pool-type structure, small amounts of gold such as verythin ribbons or foils, or even small diameter wires, can be used. Thisswimming-pool structure approach is totally unlike anything in the priorart, as gold, for example, a gold braze, is always free to flow and usedin large quantities to be effective. Accordingly, the filter capacitorof FIG. 72B provides excellent attenuation at all frequencies up to 3GHz, or even 10 GHz and beyond, thereby, attenuating undesirableinterferences from, for example, cellular telephones, microwave ovensand the like.

The attachment to an oxide-resistant metallurgically bonded surface 248,250, such as a gold braze or a gold pocket-pad, is very important toproperly ground the feedthrough filter capacitor 210′. In the prior art,the inventors know of one attempt to eliminate an attachment to gold andinstead clean the titanium surface of the titanium ferrule 134 so that astripe of a thermal-setting electrically conductive adhesive can bepainted on the surface of the titanium (the painted thermal-settingelectrically conductive adhesive stripe is typically known as an ECAstripe). The problem with an ECA stripe painted directly on the surfaceof a cleaned titanium is that a titanium metal easily re-oxidizes. Infact, a surface titanium oxide film forms almost instantly when a freshtitanium metal surface is exposed to air and/or moisture. Even a damagedtitanium oxide film can generally re-heal itself instantaneously if evenat least traces (that is, a few parts per million) of oxygen or waterare present in an environment. Researchers have proven that within amillisecond of exposure to air, a 10 nm oxide layer will be formed on acut surface of exposed essentially pure titanium metal, which will growto about 100 nm thick within a minute. Hence, a first problem of an ECAstripe directly applied to a cleaned titanium surface results from theECA stripe typically being cured at a high-temperature, between 200° C.and 300° C., in air. Thus, during curing in air, a titanium oxidere-forms on the surface of a cleaned titanium between the ECA stripe andthe bulk titanium of the ferrule. A second problem of an ECA stripe isdue to an oxygen release from the ECA during curing in addition to theair environment thereof. It is known that elevated temperature exposureof an ECA, such as an epoxy or a polymer, allows release or outgassingof oxygen and/or oxygen-containing constituents or residues that may bepresent within the ECA material. Hence, this added exposure to releasedoxygen or oxygen-containing constituents from the ECA stripe furthercauses a thickening of the oxide layer resultant from curing the ECAstripe in air. A third problem regarding ECA stripes is that thefiltered feedthrough 122 of FIG. 72B is designed to be laser welded intoan opening of an active implantable medical device housing, for example,an opening in the housing of a cardiac pacemaker. Laser welding impartsa very high temperature rise to occur in the area of the ECA stripeconnecting the feedthrough filter capacitor 210′ to the titanium ferruleof a hermetic feedthrough 132 (not labelled). Heating of an epoxy or apolymer during laser welding is sufficient to raise the temperature at,near or adjacent the laser weld such that a further release of oxygen oroxygen-containing constituents or residues, including any moisture (H₂O)associated with said epoxy or polymer, further contributes to oxidizingthe titanium metal between the ECA stripe and the surface of the ferrule134. As such, titanium oxides can be removed mechanically or chemicallyfrom a titanium ferrule by either abrasive grit blasting, such as byalumina blasting, mechanical grinding, sanding processes, hydrofluoricacid cleaning, or combinations thereof; however, the titanium oxidestypically re-form due to titanium being a highly reactive material thathas an extremely high affinity for oxygen. While a titanium oxide layeron the highly reactive titanium metal surface imparts good corrosionbehavior and high biocompatibility, the titanium oxide layer can anddoes negatively impact AIMD EMI filter performance, the negative impactbeing particularly observable at higher frequency applications. Whentitanium oxides develop between an ECA stripe and the cleaned titaniumsurface of the ferrule of a hermetic feedthrough, the equivalent seriesresistance (ESR)/insertion loss (IL) of the EMI filter can dangerouslyincrease due to the very presence of the titanium oxides such that EMIfiltering is compromised. Such ESR/IL increases are particularlyobservable at frequencies above 10 MHz. Of particular significance, isthat such ESR/IL increases (in other words, EMI capacitor ohmic losses)are often masked at low frequencies by an EMI filter's dielectriclosses. Such masking is particularly egregious to present day pacemakersand implantable cardioverter-defibrillators, which areconsidered/labelled MRI conditionally approved, as in an MRIenvironment, EMI filters divert substantial, potentially dangerous, RFcurrent generated in implanted therapy delivery leads of an AIMD duringMRI to the AIMD housing for dissipation. Hence, reliance solely on ECAstripe direct attachment to an oxidizable metal surface, such as atitanium surface, is considered to be dangerous and of poor practice bythe inventors. It is also important to note that titanium oxides canalso compromise performance in switching applications, couplingapplications, and bypass applications in addition to EMI filteringapplications.

In summary, the oxide-resistant pocket-pads 248, 248′, 250, 250′ of thepresent invention prevent re-oxidation of a cleaned titanium surface, assuch oxide-resistant pocket-pads provide a metallurgical bond to thebase metal of the ferrule that affords a reliable, long-term, stable,and low impedance electrical connection to the ground capacitormetallization 166 of the feedthrough filter capacitor 210′. A reliable,long-term, stable, and low impedance electrical connection to the groundcapacitor metallization 166 of the feedthrough filter capacitor 210′ tothe hermetic feedthrough 132 is particularly important for modernpacemakers and defibrillators, which are now generally labelled MRIconditionally approved. As previously disclosed, in an MRI environment,the feedthrough capacitor 210′ diverts a very large amount of RF currentthat is picked up by the implanted leads during an MRI scan to thehousing of the AIMD. Accordingly, a great deal of RF current passesdirectly through the ground capacitor metallization 166, through theelectrical attachment material 152, to the oxide-resistant goldpocket-pad 248, 250, and, in turn, to the ferrule 134 for dissipation bythe AIMD housing to which the ferrule is laser welded. Thus, theconductive housing of the AIMD acts as an overall energy dissipatingsurface for this diverted MRI energy, and, as previously stated, relyingsolely on a thermal-setting conductive adhesive attachment to anoxidizable surface like titanium, is considered to poor practice anddangerous.

FIG. 72C is similar to FIG. 72B except that the ground capacitormetallization (termination) 166 is along two short ends of the filtercapacitor 210′ and electrical attachment is made to a gold braze 154 aof the heretic feedthrough 132 (not labelled). The electrical attachmentto a gold braze is disclosed in U.S. Pat. No. 6,765,779, the content ofwhich is fully incorporated herein by this reference. In accordance withthe present invention, the feedthrough filter capacitor 210′ extendsbeyond the edges of the width of (in other words, overhangs) the ferruleas shown, thereby increasing the capacitors effective capacitance areaor ECA. This is particularly important for enabling filter capacitorsthat have a dielectric constant less than 1,000 k or even less than 500k as larger electrode plates can be made. Alternatively, the feedthroughfilter capacitor 210′ may only extend to the edges of the width of theferrule. Another alternative embodiment is that one side of thefeedthrough filter capacitor 210′ may extend to an edge of the width ofthe ferrule while the opposite side of the feedthrough filter capacitor210′ overhangs the edge of the width of the ferrule.

FIG. 73 is a cross-section taken generally from section 73-73 of FIG.72B illustrating a feedthrough filter capacitor 210′, including itsinternal electrode plates. The ground electrode plates are labelled 146and the active electrode plates are labelled 144. Importantly, thecapacitor's ground electrode plates 146 are attached to a groundcapacitor metallization (termination) 166 using an electricallyconductive material 152, which at least partially connects to anoxide-resistant pocket-pad 248 (not labelled) such as gold braze or agold pocket-pad 250.

Referring once again to FIG. 73, it is noted that a dramatic improvementin volumetric efficiency of the filter capacitor 210′ is achievedbecause the filter capacitor is much wider in size, therefore, theoverlap of the interleaved electrode plates 144 and 146 is also muchgreater. The larger sized electrode plates due to the increased filtercapacitor width thereby increases the capacitor's “effective capacitancearea” (ECA). Increased ECA, s previously disclosed, is particularlyenabling for a filter capacitor having dielectric constant k less than1,000 or 500. By increasing the ECA of low k filter capacitors, one canachieve the required capacitance value needed to effectively filter EMIwithout sacrificing EMI filter reliability. In this embodiment, becausethe filter capacitor 210′ is wider, the ground capacitor metallizations166 are electrically connected to the oxide-resistant pocket-pads 250,which can be gold or gold braze pocket-pads. The oxide-resistantpocket-pads 250 enable attachment of a wider filter capacitor 250′ tothe hermetic feedthrough 132 such that both an increased ECA and anoxide-resistant electrical attachment to the ferrule 134 is achieved.Looking closely at the left-hand side of the ferrule 134 of the hermeticfeedthrough 132, one can see that the oxide-resistant pocket-pad 250 isrounded and on the right-hand side of the ferrule 134 of the hermeticfeedthrough 132, the oxide-resistant pocket-pad 250 has square corners.As previously disclosed, the oxide-resistant pocket-pads 250 can be madeby machining, stamping or metal injection molding the ferrule 134. Forexample, if machining is used, the rounded shape can easily be machinedwith a ball mill end. Additionally, either a rounded, a rectangular or asquare shaped oxide-resistant pocket-pad 250 can alternatively beachieved by stamping and metal injection molding. Also, as previouslydisclosed, the feedthrough filter capacitor 210′ may only extend to theedges of the width of the ferrule, or one side of the feedthrough filtercapacitor 210′ may extend to an edge of the width of the ferrule whilethe opposite side of the feedthrough filter capacitor 210′ may overhangthe edge of the width of the ferrule. In an embodiment, the filtercapacitor 210′ is electrically connected to both an oxide-resistantpocket-pad 250 of the ferrule 134 of the filtered feedthrough 132 and atleast a portion of the gold braze 154 a hermetically sealing theinsulator 156 and the ferrule 134 of the hermetic feedthrough 132.

Referring once again to FIG. 73, one can see that the terminal pin142,136 is continuous from the device side (142) to the body fluid side(136). The terminal pin 142,136 is gold brazed 154 b to the insulator156 such that a hermetic seal is formed. The insulator comprises viahole metallizations (not labelled) that are sputtered on the insulator156 as shown. It is understood that one or more sputter layers areapplied to the insulator via holes to facilitate wetting of a brazematerial. In some embodiments, a first sputter layer is applied to theinsulator via hole, which is an adhesion layer, and a second layer isapplied over the adhesion layer, which is a wetting layer. In someembodiments, a single layer which has both adhesion and wettingproperties is applied to an insulator via hole. Importantly,electrically conductive material 168 flows down through the passagewayof the feedthrough capacitor (also known as a feedthrough capacitor viahole) and contacts the active capacitor metallization 164 of thecapacitor via hole and the gold braze 154 b of the hermetic feedthrough132. Accordingly, an oxide-resistant electrical connection is madebetween the active capacitor metallization 164 and the gold braze 154 bof the hermetic feedthrough 132 using an electrically conductivematerial 168. An oxide-resistant electrical connection is very importantif the terminal pin 142. 136 comprises an oxidizable material, forexample, niobium, tantalum, titanium or molybdenum. The oxide-resistantelectrical connection is also particularly important if the terminalpins comprise alloys, such as platinum-iridium or palladium-iridiumalloys, as even a small percentage of iridium can cause oxidation on thesurface of the terminal pin. During the brazing process, the gold braze154 b burns through a terminal pin oxide layer thereby forming a lowresistance, low impedance metallurgical bond to the base metal of saidterminal pin. Attaching the active capacitor metallization of acapacitor via hole to the gold braze of a terminal pin of a hermeticfeedthrough is more thoroughly disclosed in U.S. Pat. No. 6,888,715, thecontent of which is fully incorporated herein by this reference.

FIGS. 74A, 74B and 74C are taken from FIGS. 32A, 32B and 32C of U.S.Provisional application, Ser. No. 62/646,552 (the '552 provisional).These figures illustrate an internally grounded feedthrough filtercapacitor 210′i that has no diameter or perimeter metallization at all.In other words, the electrode ground plates of the filter capacitor210′i are grounded through a ground terminal pin 142gnd. Referring toFIG. 74C, it is appreciated that, since there is no need for anyexternal ground capacitor metallization for electrical connectionbetween the feedthrough capacitor and the ferrule, the need for the goldpocket-pads of the ferrule is also completely eliminated. However,importantly, it is also appreciated that, for a low k filter capacitork<1,000, to substantially increase the ECA of the filter capacitor, saidfilter capacitor of FIG. 74C can be designed to significantly overhangthe ferrule in either the width, the length or both the width and lengthdimensions. Accordingly, internally grounded feedthrough filtercapacitors in combination with low k dielectric filter capacitorsk<1,000 can be designed to fit very tight geometries characteristicinside the hermetically sealed housing of modern AIMDs.

FIG. 75 is taken from FIG. 37 of the '552 provisional. In thisembodiment, illustrated is a long rectangular feedthrough filtercapacitor 210′h, which comprises and internal ground terminal pin 142gndand external end ground capacitor metallizations 166. This embodiment isa hybrid filter capacitor, as the filter capacitor 210′h comprises bothinternal and external grounding technologies. Hybrid filter capacitorsare best understood by referring to the cross-sectional view shown inFIG. 76 taken from FIG. 38 of the '552 provisional.

Referring back to FIG. 75, it is understood that other shapes can beused for this filter capacitor embodiment such as previously disclosed,meaning that the filter capacitor of FIG. 75 can be flush with the edgeof the ferrule of the hermetic feedthrough, or alternatively overhangone or more edges of the ferrule of the hermetic feedthrough. Forexample, the rectangular-shaped capacitor can have rounded corners.Alternatively, the capacitor can even be round, oblong (racetrack) orany other geometric shape possible, where a portion of the capacitor iseither flush with or overhangs the edges of the ferrule to greatlyincrease the ECA of the filter capacitor. It is understood thatoxide-resistant attachments can also similarly be made.

FIG. 76 is taken from cross-section 76-76 of FIG. 75 showing theinternal construction of the hybrid feedthrough filter capacitor 210′h.Illustrated in more detail are the ground electrode plates 146 andactive electrode plates 144 of the hybrid filter capacitor. In thecenter of the hybrid filter capacitor, one can see a ground terminal pin142gnd, which is gold brazed 154 b′ to either a peninsula 139 or abridge 141 embodied by the ferrule 134. Importantly, ground terminal pin142gnd is attached in a very low resistance and low impedance manner sothat the hybrid filter capacitor can divert high frequency RF energythrough the ground terminal pin 182gnd to the ferrule 134 and then, inturn, to the AIMD housing (not shown). It is appreciated that all theferrule embodiments disclosed herein are configured to be laser weldedinto an opening of the housing of an AIMD; however, it is understoodthat the ferrule may be co-formed with the housing of the AIMD, or aferrule may be entirely omitted, with the insulator of the hermeticfeedthrough being directly hermetically sealed to the AIMD housingitself.

Referring once again to FIG. 76, one can see that the ground electrodeplates 146 are electrically connected to the internal ground terminalpin 142gnd and to the external metallizations 166 on opposite ends ofthe rectangular hybrid filter capacitor as shown. These ground capacitormetallizations 166 are electrically connected to the noveloxide-resistant pocket-pads 250 using an electrically conductivematerial 152. Hence, the term “hybrid” internally grounded filtercapacitor 210′h, as the ground electrode plates are grounded both to theground terminal pin 142gnd and to the external ground capacitormetallizations 166. Hybrid filter capacitor electrical connections areparticularly enabling when the filter capacitor becomes long, and theactive terminal pins are a substantial distance (a long way or distant)from the ground terminal pin 142gnd, as the inductance and theresistance can build up across the ground electrode plates such that theinsertion loss or filter performance of the terminal pins furthest awayfrom the ground terminal pins 142gnd is degraded. Referring once againto FIG. 76, it is also appreciated that additional ground terminal pins142gnd can be added as necessary for optimal filter performance. Inaccordance with the present invention, one can see that the filtercapacitor of FIG. 76 has a high number of internal electrode plates,which is essential to drive down its equivalent series resistance (ESR).

FIG. 77 is taken from FIG. 41 of the '552 provisional, which illustratesthat instead of ground terminal pins, the insulator has co-sinteredpaste-filled vias. In this embodiment, the co-sintered paste-filled viascomprise a ceramic reinforced metal composite (CRMC) 185 havingessentially pure platinum end caps 187. Referring back to FIG. 77, it isappreciated that the co-sintered paste-filled via can alternatively beentirely replaced by a substantially pure platinum (Pt), as described inU.S. Pat. Nos. 8,653,384 and 9,492,659, the contents of which are fullyincorporated herein by these references. The CRMC 185 may also comprisea CERMET. Additionally, the co-sintered paste-filled vias of the presentapplication may further comprise any of the CRMC/Pt paste-filled viaembodiments disclosed in the '552 provisional. Novel oxide-resistantpocket-pads 250 and 250′ are provided for grounding the internallygrounded feedthrough filter capacitor 210′i of FIG. 77. In thisembodiment, the feedthrough filter capacitor also has solid-filled vias119′, 119″, 199gnd, and an electrical connection material 203, which canbe a BGA, microdots or solder bumps. The electrical connection materialfurther comprises one of a solder, a thermal-setting conductiveadhesive, a thermal-setting conductive epoxy or combinations thereof. Assuch, the feedthrough filter capacitor 210′i can be electricallyconnected to both the grounding oxide-resistant pocket-pads 250, forexample a gold pocket-pad, and also to the active co-sinteredpaste-filled vias in one operation. Referring once again to FIG. 77, itis appreciated that because of the presence of the oxide-resistantpocket-pads, the filter capacitor can be made substantially wider thanthe width of the ferrule, thereby keeping the height of the filtercapacitor relatively low while increasing the volumetric efficiency ofthe filter capacitor for use in an AIMD. Referring again to FIG. 77,because the internally grounded feedthrough capacitor does not have anyexternal capacitor metallization and therefore no external electricalconnection material for attaching to the ferrule, the filter capacitoris mechanically free to float during laser welding of the hermeticfeedthrough 132 into an opening of the AIMD housing 124. The laser weldis labelled 157. Since the laser welding can cause a great deal of heatand thermal stress, it is advantageous for the internally groundedfeedthrough filter capacitor 210′i to be free floating during such laserwelding. Experiments by the inventors have shown that the absence ofelectrical connection material mitigated thermal coefficient ofexpansion mismatch of the filtered feedthrough, and in particular, ofthe filter capacitor 210′i itself, due to heat imparted during laserwelding. Moreover, because there is no electrical connection materialrequired, the feedthrough filter capacitor can not only extend to theedges of the length and the width of the ferrule, but also can overhangthe edges of both the length and the width of the ferrule, therebyproviding increased ECA.

FIG. 78 is taken from FIG. 41B of the '552 provisional. FIG. 78 issimilar to FIG. 77, except that all of the electrical connections are byway of an anisotropic conductive film (ACF). The novel nail-head 261 ofthe leadwires shown are pre-assembled to the feedthrough filtercapacitor and stand proud of said feedthrough filter capacitor, thereby,providing a mating surface in which the conductive particles within theACF can be compressed to form an electrical connection between thenail-heads of the leadwires and the platinum cap of the co-sinteredpast-filled vias as shown. Referring again to FIG. 78, it is appreciatedthat, while the feedthrough filter capacitor in this embodiment is shownhaving the same width as the width of the ferrule, the filter capacitorcan alternatively overhang the width of the ferrule. Again, this isparticularly important for filter capacitors having low k dielectricconstants k<1,000.

FIG. 79 is taken from FIG. 48 of the '552 provisional illustrating afilter circuit board 130 disposed on one of the ferrule 134, theinsulator 156, or both the ferrule and the insulator of the hermeticfeedthrough 132. The filter circuit board 130 may alternatively bedisposed adjacent on one of the ferrule 134, the insulator 156, or boththe ferrule and the insulator of the hermetic feedthrough 132.Illustrated are various exemplary embodiments of co-sinter paste-filledvia conductive pathways extending to the device and the body fluid sidesof the insulator 156 of the hermetic feedthrough 132 (not labelled). Itis understood that the co-sintered paste-filled via conductive pathwaysmay have numerous combinations of CRMC, CERMETS, pure platinum, solidwires, terminal pins, leadwires, two-part pins, metal inserts and thelike to form various conductive pathway configurations. One is referredto the '552 provisional for additional detail regarding co-sinterpaste-filled via conductive pathways. Importantly, the filter circuitboard 130 and its associated leadwires 142 are each electricallyconnected to a corresponding conductive pathway of the insulator asillustrated. In this exemplary embodiment, the filter circuit board 130has at least one internal ground electrode plate 161. A low impedanceand low resistance electrical connection is made from the internalground electrode plate 161 of the filter circuit board 130 through thecircuit board ground vias through an electrical connection material 203to oxide-resistant pocket-pads 250 to the ferrule 134 as illustrated. Itis appreciated that 2, 3 or “n” number of ground electrode plates 161can be disposed on the surface of the filter circuit board 130 orembedded within the body of the filter circuit board 130 or bothdisposed on the surface of the circuit board and embedded within thebody of the circuit board. In an embodiment, there are at least twointernal ground electrode plates and at least one external groundelectrode plate, the at least one external ground electrode plate beingdisposed between the filter circuit board and the device side of theinsulator and/or the ferrule of the hermetic feedthrough.

Also illustrated in FIG. 79 are filter capacitors electrically connectedto the active terminal pins (there are 6 shown in this exampleembodiment) and to the ground via holes of the filter circuit board 130.The filter circuit board illustrated has one filter circuit board groundelectrode plate 161. It is noted that the filter circuit board 130 ofthe present application comprises at least one filter circuit boardground electrode plate. The at least one filter circuit board groundelectrode plate may be either an external ground electrode plate(meaning that the ground electrode plate is disposed on the filtercircuit board) or an internal ground electrode plate (meaning that theground electrode plate is embedded within the body of the circuitboard). Each filter capacitor of the filter circuit board is configuredto divert high frequency energy from the active terminal pins 142 athrough 14 f to the ferrule 134 of the hermetic feedthrough 132 (notlabelled) to the AIMD housing (not shown), the ferrule and housing beingthe AIMD ground. The filter capacitors of the present application areselected from the group consisting of an MLCC chip capacitor 210, an X2Yattenuator 210″, a flat-through capacitor 210″, or combinations thereof.

Referring back to FIG. 79, it is understood by those skilled in the artthat a wire 187W of a conductive pathway of the hermetic feedthrough canbe extended beyond the thickness of the insulator 156 of the hermeticfeedthrough to the body fluid side, to the device side, or both to thebody fluid and device sides of said hermetic feedthrough for attachmentto either internal circuits of the AIMD or to the connectors or otherelectronic components of the header block. Furthermore, the CRMC 185 orthe CRMC 185 and the Pt 187 materials of the co-sintered paste-filledvias illustrated may be replaced entirely by only an essentially pureplatinum co-sintered paste-filled via as disclosed by the incorporatedU.S. Pat. Nos. 8,653,384 and 9,492,659. The far-right co-sinteredpaste-filled via is exemplary of an essentially pure platinum 187co-sintered conductive pathway of a hermetic feedthrough.

FIG. 80 is taken from FIG. 129 of U.S. Pat. No. 10,272,253, referred tohereinafter as the 253 patent, the content of which is fullyincorporated herein by this reference. FIG. 80 illustrates a general topview of an exemplary embodiment of the filter circuit board 130 of FIG.79. In this exemplary embodiment, the MLCC chip capacitors 210 areelectrically connected to the active terminal pins 142 a through 142 fand to the ground via holes 163 a through 163 f using circuit tracesdisposed on the filter circuit board 130.

FIG. 81, which is taken from FIG. 130 of the '253 patent, is a sectionalview of 81-81 of FIG. 80. Illustrated is a ground electrode plate 161electrically connected to each of the ground via holes of the filtercircuit board 130 (not labelled). Accordingly, each one of the MLCC chipcapacitors 210 of filter circuit board of FIG. 80 is physically disposedvery close to their corresponding ground via hole 163 a through 163 fand is electrically connected in a low resistance and low impedancemanner through the ground via holes 163 a through 163 f of the filtercircuit board to the co-sintered paste-filled via active conductivepathways of the hermetic feedthrough forming the filtered feedthrough122 as shown. Referring back to FIG. 80, the circuit traces of thefilter circuit board have active circuit traces 205 and ground circuittraces 207. It is contemplated that the MLCC chip capacitor can bepositioned on the filter circuit board such that the length of theactive circuit trace 205 can be shortened while the ground circuit trace207 can be lengthened. It is also contemplated that by simply moving orrealigning the MLCC chip capacitor, the ground circuit trace 207 can becompletely eliminated. By moving or realigning the MLCC chip capacitor,the ground termination 166 of each MLCC chip capacitor 210 can butt upand directly be attached to their corresponding ground via hole 163 athrough 163 f making the ground electrical connection. It is alsocontemplated that by rotating and lengthening the MLCC chip capacitor,the active circuit trace 205 can also be eliminated. By rotating andlengthening the MLCC chip capacitor 210, the active termination 164 ofthe MLCC chip capacitor can butt up and directly be attached to theircorresponding active terminal pins 142 a through 142 f making the activeelectrical connection. As such, re-positioning and/or changing the sizeof the MLCC chip capacitor and/or adjusting the length of or eliminatingeither the active circuit trace 205 or the ground circuit trace 207 orboth the active circuit trace 205 and the ground circuit trace 207allows circuit board design flexibility, which can be important, forexample, when size limitations or enhanced filter performance arerequired.

FIG. 82, which is taken from FIG. 131 of the '253 patent, is a sectionalview of 82-82 of FIG. 80. Illustrated is a filtered feedthrough 122having ground terminal pins attached to the ferrule 134 of a hermeticfeedthrough (not labelled). On the left-hand side of FIG. 82, a groundterminal pin 142gnd is brazed into a via hole that extends through thethickness of the ferrule 134. On the right-hand side of FIG. 82, aground terminal pin 142′gnd is attached within a counterbore of theferrule 134. It is contemplated that more than two or “n” number ofground terminal pins may be brazed into a ferrule 134 of a hermeticfeedthrough 132. Further, it is contemplated the hermetic feedthroughmay have ground terminal pin embodiments that are the same or differentpending the requirement of the application. The embodiments of FIG. 82are not limiting. It is contemplated that the ground terminal pins mayalternatively be attached to a peninsula or a bridge of a ferrule, topocket-pads residing on or in a ferrule, or combinations thereof, sothat a ground electrical connection can be made to the filter circuitboard of a filtered feedthrough. While FIG. 82 shows ground terminalpins attached to the ferrule, it is understood that the ground terminalpins may be replaced with filled ground vias. Additionally, a filteredfeedthrough may comprise a ferrule having any number and or combinationof ground terminal pins and ground filled vias for grounding.

FIG. 83 taken from FIG. 132 of the '253 patent is a sectional view of83-83 of FIG. 80 illustrating the ground electrical connections 163 b,163 d and 163 f to respective MLCC chip capacitors 210.

FIG. 84 is similar to FIG. 159 of the '253 patent except that FIG. 84has an active terminal pin passing all the way through the conductivepathway of the insulator 156 of the hermetic feedthrough. It is notedthat the active terminal pin is labelled 142 on the device side and 136on the body fluid side. The terminal pin is shown gold brazed 154 b tosputtered metalized surfaces of the alumina insulator 156, therebyhermetically sealing the terminal pin 142,136 and the insulator 156.Referring once again to FIG. 84, one can see that there is a goldmeniscus 154 b′ that forms at the terminal pin 142 during the hightemperature gold brazing operation. The gold meniscus 154 b′ provides anelectrical connection 145 between the filter capacitor 210 activecapacitor metallization 164 and the gold braze meniscus 154 b′ as shown.The gold braze electrical connection 145 enabled by the gold brazemeniscus 154 b′ is important because attaching to an oxide-resistantmaterial, such as the gold braze meniscus 154 b′, makes a low resistantand low impedance electrical connection between the capacitor activetermination 164 and the feedthrough pin 142. Moreover, suchoxide-resistant electrical connections enable the use of highlyoxidizable terminal pins 142,136, for example, niobium, tantalum,molybdenum or the like.

FIG. 78 is taken from FIG. 41B of the '552 provisional. FIG. 78 issimilar to FIG. 77, except that all of the electrical connections are byway of an anisotropic conductive film (ACF) 213′. The novel nail-head261 of the leadwires shown are pre-assembled to the feedthrough filtercapacitor and stand proud of said feedthrough filter capacitor, thereby,providing a mating surface in which the conductive particles within theACF can be compressed to form an electrical connection between thenail-heads of the leadwires and the platinum cap of the co-sinteredpast-filled vias as shown. Referring again to FIG. 78, it is appreciatedthat, while the feedthrough filter capacitor in this embodiment is shownhaving the same width as the width of the ferrule, the filter capacitorcan alternatively overhang the width of the ferrule. Again, this isparticularly important for filter capacitors having low k dielectricconstants k<1,000.

FIG. 85 is taken from FIG. 23 of U.S. Pat. No. 10,272,252, hereinafterreferred to as '252 patent, the content of which is fully incorporatedherein by this reference. It is contemplated that the present inventionapplies to any of the embodiments disclosed in the '252 patent.Referring to FIG. 85, illustrated is a novel two-part pin residingwithin a conductive pathway of a filtered feedthrough 122 (notlabelled). Because the conductive pathway of the hermetic feedthroughcomprises a two-part pin, the body fluid side of the hermeticfeedthrough can comprise a first terminal pin 136 that is low cost butbiocompatible, such as niobium, tantalum, titanium, molybdenum or thelike. The second pin 117 of the two-part pin can then be anoxide-resistant terminal pin, for example, platinum, palladium or alloysthereof, so that a low resistance and low impedance electricalconnection can be made when the filter capacitor is attached to thehermetic feedthrough, thereby forming a filtered feedthrough. Asillustrated in FIG. 85, a gold braze 154 b co-joins and co-brazes thebody fluid side terminal pin 136 to the device side terminal pin 117. Inan embodiment (shown on the right side of FIG. 85), the two-part pin maybe joined, for example by welding 424, before co-brazing. The deviceside terminal pin 117 is shown as a short pin to which a third pin isprovided within the capacitor conductive pathway of a feedthrough filtercapacitor 210′. The third pin is attached to the two-part of thehermetic feedthrough using an electrically conductive material 168 asillustrated. In this embodiment, therefore, the third pin can be lowcost pin 142 or leadwire, such as copper, aluminum, copper-beryllium,tin-copper, that can then be routed to the device electronic circuits(such as the device circuit board not shown). Alternatively, the deviceside terminal pin 117 of the hermetic feedthrough may optionally extendall the way through the conductive pathway of the feedthrough filtercapacitor 210′ for attachment to the AIMD electronics, therebyeliminating the third pin. The feedthrough filter capacitor 210′ of FIG.85 is a conventional filter capacitor having an external or perimeterground capacitor metallization. Shown is a ground electrical connectionbetween the external or perimeter ground capacitor metallization of thefilter capacitor 210′ and the gold braze 154 a hermetically sealing theferrule 134 to the insulator 156 of the hermetic feedthrough using anelectrically conductive material 152. The electrically conductivematerial 152 contacts at least a portion of the gold braze 154 a. Aspreviously disclosed, electrical connection may alternatively be to agold pocket-pad. It is appreciated that the feedthrough filter capacitor210′ can alternatively be an internally grounded filter capacitor 210′i,thereby eliminating the need for an external ground electricalconnection.

FIG. 85 also shows an insulator metallization 177, 179 at leastpartially disposed on the perimeter surface of the insulator 156. Afirst gold braze 154 a hermetically seals the ferrule 134 to theinsulator metallization. The insulator metallization may comprise anadhesion layer 177 and a wetting layer 179, wherein the adhesion layeris disposed on the insulator and the wetting layer is disposed on theadhesion layer; however, the insulator metallization may comprise onelayer having both adhesion and wetting properties. The insulatormetallization may further comprise a titanium adhesion layer and amolybdenum and/or a niobium wetting layer.

FIG. 86 is a flow chart taken from FIG. 165 of U.S. Pat. No. 10,249,415,the content of which is fully incorporated herein by this reference. Apressing (also known as a second lamination step or second pressingstep) is shown between the “Fill with Pt paste” and “Singulate” methodsteps. The inventors have discovered that this second pressing step isvery important as the second pressing step forces the conductive viafilled pastes into every opening, nook and cranny along theirinterfaces, facilitating co-sintering. This second pressing step is alsoimportant as the intimacy provided between the ceramic insulator and theconductive paste permits diffusion and bonding of the ceramic and theconductive paste along their interface, which is disclosed in moredetail below.

Referring once again to FIG. 86, during the “Fill with CRMC” step, atleast some small air cavities or vacancies are created. The “Dry” stepprepares the insulator paste-filled vias for drilling so that a platinumpaste can be added, which may create yet more air pockets or voids. Theaddition of a second pressing step, wherein an entire green bar orinsulator body is pressed under very high pressure, by either mechanicalor isostatic pressing, forcing compaction and flow of the CRMC 185and/or the platinum 187 pastes to fill and close such voids, therebyforming a more solid void-free or air pocket-free green bar orinsulator. The laminated green bar of insulator body can then besingulated and fired.

FIG. 87 is a cross-sectional perspective of a laminate embodiment thatillustrates stacked laminated sheets prior to the second “Pressing” stepin accordance with the left-hand side of the flow chart FIG. 86. Thedashed lamination lines 216 indicate the layers of stacked sheets. It isunderstood that the insulator may comprise a single solid green body(see the right-hand side of the flow chart of FIG. 86), thus the dashedlamination lines 216 of FIG. 87 would not be present.

FIG. 87 is idealized, in that, it shows an alumina substrate 156 thathas a drilled via hole that is completely filled with a paste comprisingCRMC 185, is then dried, drilled and re-filled again with a pastecomprising pure platinum or substantially pure platinum 187. At veryhigh magnification levels, one would see air bubble, voids or openpockets along the interface between the CRMC 185 and the alumina 156 andbetween the platinum 187 and the CRMC 185 pastes.

FIG. 88 shows what happens to FIG. 87 after the addition of the novelsecond “Pressing” step (second lamination step). The laminated bar ispressed a second time under high pressure to fill and close the bubbles,voids and pockets, in preparation for singulation and firing. The effectof this is to force integration of the materials such that an integratedmixing zone is made. As shown, there are actually two mixing zones. Thefirst mixing zone 222 is between the green alumina insulator 156 and theCRMC 185 paste. A second mixing zone 226 is between the CRMC 185 and thesubstantially pure platinum 187 pastes. By driving these materials andintermixing them prior to sintering, an intimacy between the alumina andthe CRMC and between the CRMC and the pure platinum is achieved,facilitating diffusion and bonding at the interfaces of these materialsthereby providing a more robust hermetic seal.

It is understood to those skilled in the art that the novel secondpressing step has wide applicability to a number of other teachings. Inparticular, this process comprising the novel second pressing step isapplicable to U.S. Pat. Nos. 8,653,384; 8,938,309; 9,233,253; 9,352,150;9,511,220; 9,889,306; 9,993,650 and 10,272,253, U.S. Patents, thecontents of which are fully incorporated herein by these references.Referring now to U.S. Pat. No. 9,889,306 disclosing co-sintered viashaving conductive inserts, it is appreciated that the novel secondpressing step of FIG. 86 may alternatively be accomplished prior tocounter-boring or adding a metal insert.

Although several embodiments of the invention have been described indetail for purposes of illustration, various modifications of each maybe made without departing from the spirit and scope of the invention.Accordingly, the invention is not to be limited, except as by theappended claims.

What is claimed is:
 1. A filtered feedthrough for an active implantablemedical device (AIMD), the filtered feedthrough comprising: a) ahermetic feedthrough, comprising: i) an electrically conductive ferrulecomprising a ferrule opening; ii) an insulator residing in the ferruleopening where a first hermetic seal hermetically seals the insulator tothe ferrule, wherein at least one insulator passageway extends throughthe insulator to an insulator body fluid side surface opposite aninsulator device side surface, and wherein, when the ferrulehermetically sealed to the insulator is attached to an opening in anAIMD housing, the insulator body fluid side surface and the insulatordevice side surface reside outside and inside the AIMD, respectively;and iii) a platinum-containing active conductive pathway hermeticallysealed to the insulator in the at least one insulator passageway andextending from an active pathway body fluid side to an active pathwaydevice side, the active conductive pathway being in a non-conductiverelationship with the ferrule and being characterized as having been aplatinum-containing paste filled into the at least one insulatorpassageway and then co-sintered with the insulator when the insulator isin a green-state; and b) at least one flat-through filter capacitordisposed on or adjacent to the insulator device side surface of thehermetic feedthrough, the at least one flat-through filter capacitorcomprising: i) a dielectric substrate supporting at least one activeelectrode plate interleaved between and in a capacitive relationshipwith at least two ground electrode plates, wherein the active electrodeplate has active electrode plate first and second ends; and ii) a firstactive electrode metallization electrically connected to the at leastone active electrode plate first end, a second active electrodemetallization electrically connected to the active electrode platesecond end, and a ground electrode metallization electrically connectedto the at least two ground electrode plates; and c) a first activeelectrical connection electrically connecting the active conductivepathway device side to the first active electrode metallizationelectrically connected to the at least one active electrode plate firstend; d) a second active electrical connection which is connectable fromthe second active electrode metallization electrically connected to theactive electrode plate second end of the at least one flat-throughfilter capacitor to AIMD circuits housed inside an AIMD housing; and e)a ground electrical connection electrically connecting the groundelectrode metallization to the ferrule.
 2. The filtered feedthrough ofclaim 1, wherein the first hermetic seal comprises a first gold braze.3. The filtered feedthrough of claim 1, wherein the dielectric substratehas a dielectric constant k that is greater than 0 but less than 1000.4. The filtered feedthrough of claim 1, wherein the at least oneflat-through filter capacitor is located as the first filter capacitorelectrically connected to the platinum-containing active conductivepathway at or adjacent to the insulator device side surface of thehermetic feedthrough.
 5. The filtered feedthrough of claim 1, whereinthe platinum-containing active conductive pathway of the hermeticfeedthrough comprises a co-sintered ceramic reinforced metal compositematerial or a co-sintered substantially pure platinum material that ishermetically sealed to the insulator in the at least one insulatorpassageway.
 6. The filtered feedthrough of claim 1, wherein the at leastone flat-through filter capacitor is disposed on a circuit board, andwherein at least one circuit board ground plate is disposed on or insidethe circuit board, wherein the ground electrical connection comprises afirst ground electrical connection electrically connecting the groundelectrode metallization of the at least one flat-through filtercapacitor to the at least one circuit board ground plate and a secondground electrical connection electrically connecting the at least onecircuit board ground plate to the ferrule.
 7. The filtered feedthroughof claim 1, wherein the at least one flat-through filter capacitor isdisposed at least partially over the insulator in a tombstone mountedposition with the at least one active electrode plate and the at leasttwo ground electrode plates disposed in a perpendicular orientation withrespect to the insulator device side surface of the hermeticfeedthrough.
 8. The filtered feedthrough of claim 2, wherein the groundelectrical connection electrically connects the ground electrodemetallization of the at least one flat-through filter capacitor to thefirst gold braze hermetically sealing the insulator to the ferrule. 9.The filtered feedthrough of claim 6, wherein the ground electricalconnection electrically connecting the at least one circuit board groundplate to the ferrule comprises an oxide-resistant material, theoxide-resistant material being selected from the group of: a) the firsthermetic seal hermetically sealing the insulator to the ferrule; b) atleast one oxide-resistant ground pin that is connected to the ferrule bya third second gold braze or a laser weld; c) an oxide-resistant areasupported by the ferrule, the oxide-resistant area being selected fromthe group of a gold pocket-pad, a gold pad, an oxide-resistant metaladdition, a thermal-setting electrically conductive adhesive (ECA)stripe, and combinations thereof; d) a ferrule peninsula; and e) aferrule-bridge.
 10. The filtered feedthrough of claim 9, wherein theoxide-resistant material is selected from the group of platinum, gold,tungsten, iridium, palladium, niobium, tantalum, ruthenium, rhodium,silver, osmium, and alloys and combinations thereof.
 11. The filteredfeedthrough of claim 9, wherein the at least one oxide-resistant groundpin is of a material selected from the group of platinum-rhodium,platinum-iridium, platinum-palladium, platinum-gold and naturallyoccurring alloys such as platiniridium (platinum-iridium), iridiosmiumand osmiridium (iridium-osmium).
 12. The filtered feedthrough of claim1, wherein an insulating washer is disposed between the at least oneflat-through filter capacitor and the hermetic feedthrough.
 13. Afiltered feedthrough for an active implantable medical device (AIMD),the filtered feedthrough comprising: a) a hermetic feedthrough,comprising: i) an electrically conductive ferrule comprising a ferruleopening; ii) an insulator residing in the ferrule opening where a firstgold braze hermetically seals the insulator to the ferrule, wherein atleast one insulator passageway extends through the insulator to aninsulator body fluid side surface opposite an insulator device sidesurface, and wherein, when the ferrule hermetically sealed to theinsulator is attached to an opening in an AIMD housing, the insulatorbody fluid side surface and the insulator device side surface resideoutside and inside the AIMD, respectively; and iii) aplatinum-containing active conductive pathway hermetically sealed to theinsulator in the at least one insulator passageway and extending from anactive pathway body fluid side to an active pathway device side, theplatinum-containing active conductive pathway being in a non-conductiverelationship with the ferrule and being characterized as having been aplatinum-containing paste filled into the at least one insulatorpassageway and then co-sintered with the insulator when the insulator isin a green-state; and b) at least one flat-through filter capacitordisposed on or adjacent to the insulator device side surface of thehermetic feedthrough, the at least one flat-through filter capacitorcomprising: i) a dielectric substrate supporting at least one activeelectrode plate interleaved between and in a capacitive relationshipwith at least two ground electrode plates, wherein the active electrodeplate has active electrode plate first and second ends; and ii) a firstactive electrode metallization electrically connected to the at leastone active electrode plate first end, a second active electrodemetallization electrically connected to the active electrode platesecond end, and a ground electrode metallization electrically connectedto the at least two ground electrode plates; and c) a circuit boardcomprising at least one ground electrode plate disposed on or inside thecircuit board, wherein the at least one flat-through filter capacitor isdisposed on the circuit board; d) a first active electrical connectionelectrically connecting the first platinum-containing active conductivepathway device side to the first active electrode metallizationelectrically connected to the active electrode plate first end; e) asecond active electrical connection which is connectable from the secondactive electrode metallization electrically connected to the activeelectrode plate second end of the at least one flat-through filtercapacitor to AIMD circuits housed inside an AIMD housing; f) a firstground electrical connection electrically connecting the groundelectrode metallization of the at least one flat-through filtercapacitor to the at least one circuit board ground plate; and g) asecond ground electrical connection electrically connecting the at leastone circuit board ground plate to the ferrule.
 14. The filteredfeedthrough of claim 13, wherein the platinum-containing activeconductive pathway of the hermetic feedthrough comprises a pure platinumpaste that is filled into the at least one insulator passageway and thencharacterized as having been co-sintered with the insulator when theinsulator is in a green-state to thereby hermetically seal the pureplatinum material conductive pathway to the insulator in the at leastone insulator passageway.
 15. The filtered feedthrough of claim 13,wherein the platinum-containing active conductive pathway of thehermetic feedthrough comprises a ceramic reinforced platinum compositepaste that is filled into the at least one insulator passageway and thencharacterized as having been co-sintered with the insulator when theinsulator is in a green-state to thereby hermetically seal the ceramicreinforced platinum composite material conductive pathway to theinsulator in the at least one insulator passageway.
 16. The filteredfeedthrough of claim 13, wherein an insulating washer is disposedbetween the at least one flat-through filter capacitor and the hermeticfeedthrough.
 17. The filtered feedthrough of claim 13, wherein thedielectric substrate of the at least one flat-through filter capacitorhas a dielectric constant k that is greater than 0 but less than 1000.18. The filtered feedthrough of claim 13, wherein the at least oneflat-through filter capacitor is located as the first filter capacitorelectrically connected to the platinum-containing active conductivepathway at or adjacent to the insulator device side surface of thehermetic feedthrough.
 19. The filtered feedthrough of claim 13, whereinthe second ground electrical connection electrically connecting the atleast one circuit board ground plate to the ferrule comprises anoxide-resistant material, the oxide-resistant material being selectedfrom the group of: a) the first hermetic seal hermetically sealing theinsulator to the ferrule; b) at least one oxide-resistant ground pinconnected to the ferrule by a second gold braze or a laser weld; c) anoxide-resistant area supported by the ferrule, the oxide-resistantmaterial being selected from the group of a gold pocket-pad, a gold pad,an oxide-resistant metal addition, a thermal-setting electricallyconductive adhesive (ECA) stripe, and combinations thereof; d) a ferrulepeninsula; and e) a ferrule-bridge.
 20. The filtered feedthrough ofclaim 13, wherein the second ground electrical connection electricallyconnects the at least one circuit board ground plate to the first goldbraze hermetically sealing the insulator to the ferrule.
 21. A filteredfeedthrough for an active implantable medical device (AIMD), thefiltered feedthrough comprising: a) a hermetic feedthrough, comprising:i) an electrically conductive ferrule comprising a ferrule opening; ii)an insulator residing in the ferrule opening where a first hermetic sealhermetically seals the insulator to the ferrule, wherein at least oneinsulator passageway extends through the insulator to an insulator bodyfluid side surface opposite an insulator device side surface, andwherein, when the ferrule hermetically sealed to the insulator isattached to an opening in an AIMD housing, the insulator body fluid sidesurface and the insulator device side surface reside outside and insidethe AIMD, respectively; and iii) a active conductive pathway comprisinga pure platinum material or a ceramic reinforced platinum compositematerial hermetically sealed to the insulator in the at least oneinsulator passageway, the active conductive pathway extending from anactive pathway body fluid side to an active pathway device side, whereinthe active conductive pathway is characterized as having been aplatinum-containing paste filled into the at least one insulatorpassageway and then co-sintered with the insulator when the insulator isin a green-state; and b) at least one flat-through filter capacitorcomprising: i) a dielectric substrate supporting at least one activeelectrode plate interleaved between and in a capacitive relationshipwith at least two ground electrode plates, wherein the active electrodeplate has active electrode plate first and second ends, and wherein thedielectric substrate has a dielectric constant k that is greater than 0but less than 1,000, ii) a first active electrode metallizationelectrically connected to the at least one active electrode plate firstend, a second active electrical connection electrically connected to theactive electrode plate second end, and a ground electrode metallizationelectrically connected to the at least two ground electrode plates ofthe flat-through filter capacitor, and iii) wherein the at least oneflat-through filter capacitor is disposed at least partially over theinsulator in a tombstone mounted position with the at least one activeelectrode plate and the at least two ground electrode plates disposed ina perpendicular orientation with respect to the insulator device sidesurface of the hermetic feedthrough, and iv) wherein the at least oneflat-through filter capacitor is located as the first filter capacitorelectrically connected to the active conductive pathway at or adjacentto the insulator device side surface of the hermetic feedthrough; c) afirst active electrical connection electrically connecting theplatinum-containing active conductive pathway device side of thehermetic feedthrough to the first active electrode metallizationelectrically connected to the active electrode plate first end; d) asecond active electrical connection which is connectable from the secondactive electrode metallization electrically connected to the activeelectrode plate second end of the at least one flat-through filtercapacitor to AIMD circuits housed inside an AIMD housing; and e) aground electrical connection electrically connecting the groundelectrode metallization to the ferrule.